Salt, acid generator, resist composition and method for producing resist pattern

ABSTRACT

A salt having a group represented by formula (a): 
     
       
         
         
             
             
         
       
         
         
           
             wherein X a  and X b  each independently represent an oxygen atom or a sulfur atom, X 1  represents a divalent group having an alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and where a hydrogen atom may be replaced by a hydroxy group or a fluorine atom, and * represents a binding site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Application No. 2014-170794 filed on Aug. 25, 2014. The entire disclosures of Japanese Application No. 2014-170794 is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a salt, an acid generator, a resist composition and a method for producing resist pattern.

2. Related Art

A resist composition which contains a salt represented by the following formula as an acid generator is described in Patent document of JP 2011-037837A.

SUMMARY OF THE INVENTION

The present invention provides following inventions of <1> to <11>.

<1> A salt having a group, represented by formula (a).

wherein X^(a) and X^(b) each independently represent an oxygen atom or a sulfur atom,

X¹ represents a divalent group having an alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and where a hydrogen atom may be replaced by a hydroxy group or a fluorine atom, and

* represents a binding site.

<2> The salt according to <1>, wherein

the alicyclic hydrocarbon group is an adamantyl group where a methylene group may be replaced by an oxygen atom or a carbonyl group and where a hydrogen atom may be replaced by a hydroxy group.

<3> The salt according to <1> or <2>, which has a structure represented by a formula (a1):

wherein X^(a), X^(b) and * are as defined in claim 1,

ring W represents a C₃ to C₃₆ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom, a sulfur atom, a carbonyl group or a sulfonyl group and where a hydrogen atom may be replaced by a hydroxy group, a C₁ to C₁₂ alkyl group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group, a C₆ to C₁₀ aromatic hydrocarbon group or a combination thereof.

<4> The salt according to any one of <1> to <3>, which includes an anion represented by a formula (a2:

wherein X^(a), X^(b) and * are as defined in claim 1,

ring W represents a C₃ to C₃₆ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom, sulfur atom, a carbonyl group or a sulfonyl group and where a hydrogen atom may be replaced by a hydroxy group, a C₁ to C₁₂ alkyl group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group, a C₆ to C₁₀ aromatic hydrocarbon group or a combination thereof,

L^(b1) represents a C₁ to C₂₄ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group and where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and

Q¹ and Q² independently represent a fluorine atom or a C₁ to C₆ perfluoroalkyl group.

<5> The salt according to <3> or <4>, wherein

the ring W is a ring represented by formula (a1-1), formula (a1-2) or formula (a1-3:

in each of the formulae (a1-1), (a1-2) and (a1-3), a methylene group may be replaced by an oxygen atom, a sulfur atom, a carbonyl group or a sulfonyl group, and a hydrogen atom may be replaced by a hydroxy group, a C₁ to C₁₂ alkyl group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group, or a C₆ to C₁₀ aromatic hydrocarbon group.

<6> The salt according to <4>, wherein

L^(b1) is *—CO—O—(CH₂)_(t)—,

where t represents an integer of 0 to 6, and

* represents a binding site to —C(Q¹)(Q²)-.

<7> The salt according to any one of <1> to <6>, wherein

X¹ is a divalent group represented by formula (X¹-1), by formula (X¹-2), by formula (X¹-3), or by formula (X¹-4):

wherein R¹, R², R³, R⁴, R⁵ and R⁶ each independently represent a C₅ to C₁₂ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group and where a hydrogen atom may be replaced by a hydroxy group or a fluorine atom, and

* represents a binding site to X^(a) and X^(b).

<8> An acid generator, which includes the salt according to any one of <1> to <7>.

<9> A resist composition including the acid generator according to <8> and a resin having an acid-labile group.

<10> The resist composition according to <9>, further including a salt which generates an acid weaker in acidity than an acid generated from the acid generator.

<11> A method for producing a resist pattern including steps (1) to (5);

(1) applying the resist composition according to <9> or <10> onto a substrate;

(2) drying the applied composition to form a composition layer;

(3) exposing the composition layer;

(4) heating the exposed composition layer, and

(5) developing the heated composition layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

“(Meth)acrylic monomer” means a monomer having a structure of “CH₂═CH—CO—” or “CH₂═C(CH₃)—CO—”, as well as “(meth)acrylate” and “(meth)acrylic acid” mean “an acrylate or methacrylate” and “an acrylic acid or methacrylic acid,” respectively. Herein, chain structure groups include those having a linear structure and those having a branched structure. The indefinite articles “a” and “an” are taken as the same meaning as “one or more”.

In the specification, the term “solid components” means components other than solvents in a resist composition.

<Salt (a)>

The salt of the present invention is a salt represented by the formula (a), which is sometimes referred to as “salt (a)”. The salt (a) is a salt which generates an acid by radiation such as light.

wherein X^(a) and X^(b) independently represent an oxygen atom or a sulfur atom,

X¹ represents a divalent group having an alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and where a hydrogen atom may be replaced by a hydroxy group or a fluorine atom, and

* represents a binding site.

X^(a) and X^(b) independently are preferably the same atom, and more preferably both an oxygen atom.

The divalent group represented by X¹ may have two or more of alicyclic hydrocarbon groups, preferably one or two of them.

The alicyclic hydrocarbon group is preferably an adamantyl group, and a methylene group contained in the adamantyl group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained in the adamantyl group may be replaced by a hydroxy group.

Examples of the divalent group represented by X¹ include a divalent saturated hydrocarbon group having an alicyclic hydrocarbon group, specifically a monocyclic or polycyclic divalent alicyclic saturated hydrocarbon group, a combination group having a monocyclic or polycyclic, alicyclic saturated hydrocarbon group and an alkanediyl group, and a combination group having at least three selected from among alkanediyl groups and monocyclic or polycyclic, alicyclic saturated hydrocarbon groups.

In the divalent group represented by X¹, an alicyclic saturated hydrocarbon group may be a monovalent one or a divalent one, preferably a monovalent one, and a methylene group contained in the alicyclic saturated hydrocarbon group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained therein may be replaced by a hydroxy group or a fluorine atom.

Specific examples of the monovalent alicyclic saturated hydrocarbon group include C₅ to C₁₀ cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group and cyclooctyl group; and C₈ to C₁₂ polycyclic monovalent alicyclic hydrocarbon groups such as an adamantyl group, or a norbornyl group, and those cycloalkyl and monovalent alicyclic hydrocarbon groups where a methylene group has been replaced by an oxygen atom or a carbonyl group or where a hydrogen atom has been replaced by a hydroxy group or a fluorine atom.

Specific examples of the divalent alicyclic saturated hydrocarbon group include a monocyclic divalent alicyclic hydrocarbon groups, i.e., a cycloalkanediyl group, preferably C₄ to C₈ cycloalkanediyl group, such as cyclobutane-1,3-diyl, cyclopentane-1,3-diyl, cyclohexane-1,4-diyl and cyclooctane-1,5-diyl groups; and polycyclic divalent alicyclic hydrocarbon groups, preferably C₅ to C₁₂ divalent alicyclic hydrocarbon groups, such as nobornane-1,4-diyl, nobornane-2,5-diyl, amadantane-1,5-diyl, and amadantane-2,6-diyl group.

The alicyclic hydrocarbon group is preferably a C₅ to C₁₀ cycloalkyl group where a methylene group has been replaced by an oxygen atom or a carbonyl group or a hydrogen atom has been replaced by a hydroxy group or a fluorine atom, or a C₈ to C₁₂ polycyclic monovalent alicyclic hydrocarbon groups, and it is more preferably an adamantyl group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom may be replaced by a hydroxy group. When the divalent group represented by X¹ has two or more of alicyclic hydrocarbon groups, two of the alicyclic hydrocarbon groups may form one spiro ring together. One example of such a spiro ring includes a ring consisting of one adamantane ring and one C₅ to C₁₀ cycloalkyl group where a methylene group may be replaced by an oxygen atom or a carbonyl group or where a hydrogen atom may be replaced by a hydroxy group or a fluorine atom.

For X¹, examples of an alkanediyl group include a chain alkanediyl group, preferably a C₁ to C₁₂ chain alkanediyl group, such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl groups;

and a branched alkanediyl group, preferably a C₂ to C₁₂ chain alkanediyl group, such as ethane-1,1-diyl, propane-1,1-diyl, propane-1,2-diyl, propane-2,2-diyl, pentane-2,4-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl, 2-methylbutane-1,4-diyl groups.

Among the divalent group, a C₁-C₁₂ alkanediyl group having the alicyclic hydrocarbon group is preferred, a C₁-C₆ alkanediyl group having an alicyclic hydrocarbon group is more preferred.

Specifically, the divalent group represented by X¹ has preferably an alkanediyl group where one to three of methylene groups have been replaced by an oxygen atom or a carbonyl group, more preferably an alkanediyl group where one or two of methylene groups have been replaced by an oxygen atom or a carbonyl group. In other words, the divalent group represented by X¹ preferably has an oxycarbonyl group or a carbonyloxy group, and more preferable has one or two of oxycarbonyl groups and carbonyloxy groups.

The divalent group of X¹ is preferably a divalent saturated hydrocarbon group having a C₅ to C₁₂ alicyclic hydrocarbon group, more preferably a divalent saturated hydrocarbon group having a C₅ to C₁₂ alicyclic hydrocarbon group and an oxycarbonyl group or a carbonyloxy group, still more preferably an alkanediyl group having a C₅ to C₁₂ alicyclic hydrocarbon group, further still more preferably an alkanediyl group having a C₅ to C₁₂ alicyclic hydrocarbon group and an oxycarbonyl group or a carbonyloxy group.

Specifically, the divalent group of X¹ is preferably one represented by the formula (X¹-1), the formula (X¹-2), the formula (X¹-3) or the formula (X¹-4), more preferably one represented by the formula (X¹-1) or the formula (X¹-4), and still more preferably one represented by the formula (X¹-4).

wherein R¹, R², R³, R⁴, R⁵ and R⁶ each independently represent a C₅ to C₁₂ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom may be replaced by a hydroxy group or a fluorine atom, and each of * represents a binding site to X^(a) or X^(b).

The salt (a) preferably has a group represented by the formula (a1).

wherein X^(a), X^(b), X¹ and * are as defined above, and

ring W represents a C₃ to C₃₆ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom, sulfur atom, a carbonyl group or sulfonyl group, and a hydrogen atom may be replaced by a hydroxy group, a C₁ to C₁₂ alkyl group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group, a C₆ to C₁₀ aromatic hydrocarbon group or combination thereof.

Examples of the alicyclic hydrocarbon group for the ring W include rings represented by formula (a1-1) to formula (a1-11).

In formula (a1-1) to formula (a1-11), a methylene group may be replaced by an oxygen atom, sulfur atom, a carbonyl group or sulfonyl group, and a hydrogen atom may be replaced by a hydroxy group, a C₁ to C₁₂ alkyl group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group or a C₆ to C₁₀ aromatic hydrocarbon group.

As to a substituent in the formula (a1-1) to the formula (a1-11), examples of the C₁ to C₁₂ alkyl group include methyl, ethyl, propyl, butyl, pentyl, hexyl. heptyl, octyl, nonyl, decyl, undecyl and dodecyl groups.

As to the substituent, examples of the C₁ to C₁₂ alkoxy group include methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, octyloxy, 2-ethylhexyloxy, nonyloxy, decyloxy, undecyloxy and dodecyloxy groups.

As to the substituent, examples of the C₃ to C₁₂ alicyclic group include groups represented by the formula (a1-1) to the formula (a1-11) below. * represent a binding site to the ring.

As to the substituent, examples of the C₆ to C₁₀ aromatic hydrocarbon group include phenyl and naphthyl groups.

The ring W is preferably a C₃ to C₁₈ alicyclic hydrocarbon group, more preferably a ring represented by the formula (a1-1), the formula (a1-2) or the formula (a1-3).

Any of carbon atom in the formula (a1-1) to the formula (a1-11) may be bonded to X^(a) and X^(b).

The salt (a) is preferably a salt in which a cation is an organic cation, preferably a salt of an anion having a group represented by formula (a) and a cation, more preferably a salt of an anion having a group represented by formula (a) and an organic cation.

The salt (a) preferably has an anion represented by the formula (a2).

wherein X^(a), X^(b), X¹ and W are as defined above,

L^(b1) represents a C₁ to C₂₄ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group and where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and

Q¹ and Q² independently represent a fluorine atom or a C₁ to C₆ perfluoroalkyl group.

Examples of the perfluoroalkyl group of Q¹ and Q² include trifluoromethyl, perfluoroethyl, perfluoropropyl, perfluoro-isopropyl, perfluorobutyl, perfluoro-sec-butyl, perfluoro-tert-butyl, perfluoropentyl and perfluorohexyl groups.

Among these, Q¹ and Q² independently are preferably trifluoromethyl or fluorine atom, and Q¹ and Q² both are more preferably a fluorine atom.

Examples of the divalent saturated hydrocarbon group of L^(b1) include an alkanediyl and a monocyclic or polycyclic divalent saturated hydrocarbon group, and a combination of two or more such groups.

Specific examples of the alkanediyl group include a chain alkanediyl group such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl, pentadecane-1,15-diyl, hexadecane-1,16-diyl and heptadecane-1,17-diyl groups;

a branched alkanediyl group such as ethane-1,1-diyl, a propane-1,1-diyl, propane-1,2-diyl, propane-2,2-diyl, pentane-2,4-diyl group, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl, 2-methylbutane-1,4-diyl groups;

a monocyclic divalent saturated alicyclic hydrocarbon group such as cyclobutane-1,3-diyl, cyclopentane-1,3-diyl, cyclohexane-1,4-diyl and cyclooctane-1,5-diyl groups; and

a polycyclic divalent saturated alicyclic hydrocarbon group such as nobornane-1,4-diyl, nobornane-2,5-diyl, amadantane-1,5-diyl, and amadantane-2,6-diyl groups.

Examples of the divalent saturated hydrocarbon group in which a methylene group has been replaced by an oxygen atom or a carbonyl group of L^(b1) include groups represented by formula (b1-1) to formula (b1-3). In formula (b1-1) to formula (b1-3), * represents a binding site to -W.

wherein L^(b2) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b3) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and a methylene group may be replaced by an oxygen atom or a carbonyl group;

provided that the total carbon number contained in the group of L^(b2) and L^(b3) is 22 or less;

L^(b4) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b5) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and a methylene group may be replaced by an oxygen atom or a carbonyl group;

provided that the total carbon number contained in the group of L^(b4) and L^(b5) is 22 or less;

L^(b6) represents a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

L^(b7) represents a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and a methylene group may be replaced by an oxygen atom or a carbonyl group;

provided that the total carbon number contained in the group of L^(b6) and L^(b7) is 23 or less.

In formula (b1-1) to formula (b1-3), when a methylene group has been replaced by an oxygen atom or a carbonyl group, the carbon number of the saturated hydrocarbon group corresponds to the number of the carbon atom before replacement.

For formula (b1-1) to formula (b1-3), examples of the divalent saturated hydrocarbon group include an alkanediyl and a monocyclic or polycyclic divalent saturated hydrocarbon group, and a combination of two or more such groups.

Specific examples of the alkanediyl group include a chain alkanediyl group such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl, pentadecane-1,15-diyl, hexadecane-1,16-diyl and heptadecane-1,17-diyl groups;

a branched alkanediyl group such as ethane-1,1-diyl, a propane-1,1-diyl, propane-1,2-diyl, propane-2,2-diyl, pentane-2,4-diyl group, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl, 2-methylbutane-1,4-diyl groups;

a monocyclic divalent saturated alicyclic hydrocarbon group such as cyclobutane-1,3-diyl, cyclopentane-1,3-diyl, cyclohexane-1,4-diyl and cyclooctane-1,5-diyl groups; and

a polycyclic divalent saturated alicyclic hydrocarbon group such as nobornane-1,4-diyl, nobornane-2,5-diyl, amadantane-1,5-diyl, and amadantane-2,6-diyl groups.

L^(b2) is preferably a single bond.

L^(b3) is preferably a C₁ to C₄ divalent saturated hydrocarbon group.

L^(b4) is preferably a C₁ to C₈ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom.

L^(b5) is preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L⁶ is preferably a single bond or a C₁ to C₄ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom.

L^(b7) is preferably a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and a methylene group may be replaced by an oxygen atom or a carbonyl group.

L^(b1) is preferably a group represented by the formula (b1-1) or (b1-3) more preferably one represented by the formula (b1-1).

Examples of the divalent group represented by formula (b1-1) include groups represented by formula (b1-4) to formula (b1-8).

wherein L^(b8) represents a single bond or a C₁ to C₂₂ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

L^(b9) represents a C₁ to C₂₀ divalent saturated hydrocarbon group;

L^(b10) represents a single bond or a C₁ to C₁₉ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

provided that the total carbon number contained in the group of L^(b9) and L^(b10) is 20 or less;

L^(b11) represents a C₁ to C₂₁ divalent saturated hydrocarbon group;

L^(b12) represents a single bond or a C₁ to C₂₀ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

provided that the total carbon number contained in the group of L^(b11) and L^(b12) is 21 or less;

L^(b13) represents a C₁ to C₁₉ divalent saturated hydrocarbon group;

L^(b14) represents a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group;

L^(b15) represents a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

provided that the total carbon number contained in the group of L^(b13), L^(b14) and L^(b15) is 19 or less;

L^(b16) represents a C₁ to C₁₈ divalent saturated hydrocarbon group;

L^(b17) represents a C₁ to C₁₈ divalent saturated hydrocarbon group;

L^(b18) represents a single bond or a C₁ to C₁₇ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group;

-   -   provided that the total carbon number contained in the group of         L^(b16), L^(b17) and L^(b18) is 19 or less.

L^(b8) is preferably a C₁ to C₄ divalent saturated hydrocarbon group.

L^(b9) is preferably a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b10) is preferably a single bond or a C₁ to C₁₉ divalent saturated hydrocarbon group, and more preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b11) is preferably a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b12) is preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b13) is preferably a C₁ to C₁₂ divalent saturated hydrocarbon group.

L^(b14) is preferably a single bond or a C₁ to C₆ divalent saturated hydrocarbon group.

L^(b15) is preferably a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group, and more preferably a single bond or a C₁ to C₈ divalent saturated hydrocarbon group.

L^(b16) is preferably a C₁ to C₁₂ divalent saturated hydrocarbon group.

L^(b17) is preferably a C₁ to C₆ divalent saturated hydrocarbon group.

L^(b18) is preferably a single bond or a C₁ to C₁₇ divalent saturated hydrocarbon group, and more preferably a single bond or a C₁ to C₄ divalent saturated hydrocarbon group.

Examples of the divalent group represented by formula (b1-3) include groups represented by formula (b1-9) to formula (b1-11).

wherein L^(b19) represents a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b20) represent a single bond or a C₁ to C₂₃ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom, a hydroxy group or an acyloxy group, and a methylene group contained in an acyloxy group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained in an acyloxy group may be replaced by a hydroxy group,

provided that the total carbon number contained in the group of L^(b19) and L^(b20) is 23 or less;

L^(b21) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b22) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group;

L^(b23) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom, a hydroxy group or an acyloxy group, and a methylene group contained in an acyloxy group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained in an acyloxy group may be replaced by a hydroxy group,

provided that the total carbon number contained in the group of L^(b21), L^(b22) and L^(b23) is 21 or less;

L^(b24) represents a single bond or a C₁ to C₂₀ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom;

L^(b25) represents a single bond or a C₁ to C₂₁ divalent saturated hydrocarbon group;

L^(b26) represents a single bond or a C₁ to C₂₀ divalent saturated hydrocarbon group where a hydrogen atom may be replaced by a fluorine atom, a hydroxy group or an acyloxy group, and a methylene group contained in an acyloxy group may be replaced by an oxygen atom or a carbonyl group, and a hydrogen atom contained in an acyloxy group may be replaced by a hydroxy group,

provided that the total carbon number contained in the group of L^(b24), L^(b25) and L^(b26) is 21 or less.

In formula (b1-9) to formula (b1-11), when a hydrogen atom has been replaced by an acyloxy group, the carbon number of the saturated hydrocarbon group corresponds to the number of the carbon atom, CO and O in addition to the carbon number of the saturated hydrocarbon group.

For formula (b1-9) to formula (b1-11), examples of the divalent saturated hydrocarbon group include an alkanediyl and a monocyclic or polycyclic divalent saturated hydrocarbon group, and a combination of two or more such groups.

Examples of the acyloxy group include acetyloxy, propionyloxy, butyryloxy, cyclohexyl carbonyloxy, adamantyl and carbonyloxy groups.

Examples of the acyloxy group having a substituent include oxoadamantyl carbonyloxy, hydroxyadamantyl carbonyloxy, oxocyclohexyl carbonyloxy, hydroxycyclohexyl and carbonyloxy groups.

Examples of the group represented by the formula (b1-4) include the following ones.

Examples of the group represented by the formula (b1-5) include the following ones.

Examples of the group represented by the formula (b1-6) include the following ones.

Examples of the group represented by the formula (b1-71 include the following ones.

Examples of the group represented by the formula (b1-8) include the following ones.

Examples of the group represented by the formula (b1-21 include the following ones.

Examples of the group represented by the formula (b1-9) include the following ones.

Examples of the group represented by the formula (b1-10) include the following ones.

Examples of the group represented by the formula (b1-11) include the following ones.

Examples of the anion represented by the formula (a2) include the following ones.

The cation of the salt (a) is preferably an organic cation. Examples of the organic cation include an organic onium cation, for example, organic sulfonium cation, organic iodonium cation, organic ammonium cation, benzothiazolium cation and organic phosphonium cation. Among these, organic sulfonium cation and organic iodonium cation are preferred, and aryl sulfonium cation is more preferred. Among these, more preferred are cations represented by the formula (b2-1) to (b2-4), which cations are sometimes referred to as “cation X” where X represents the formula number of the cation.

wherein R^(b4), R^(b5) and R^(b6) independently represent a C₁ to C₃₀ aliphatic hydrocarbon group, a C₃ to C₃₆ alicyclic hydrocarbon group or a C₆ to C₃₆ aromatic hydrocarbon group, a hydrogen atom contained in an aliphatic hydrocarbon group may be replaced by a hydroxy group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group or a C₆ to C₁₈ aromatic hydrocarbon group, a hydrogen atom contained in an alicyclic hydrocarbon group may be replaced by a halogen atom, a C₁ to C₁₈ aliphatic hydrocarbon group, a C₂ to C₄ acyl group or a glycidyloxy group, a hydrogen atom contained in an aromatic hydrocarbon group may be replaced by a halogen atom, a hydroxy group or a C₁ to C₁₂ alkoxy group, or R^(b4) and R^(b5) may be bonded together with a sulfur atom bonded thereto to form a sulfur-containing ring, a methylene group contained in the ring may be replaced by an oxygen atom, a sulfur atom or a carbonyl group;

R^(b7) and R^(b8) in each occurrence independently represent a hydroxy group, a C₁ to C₁₂ aliphatic hydrocarbon group or a C₁ to C₁₂ alkoxy group,

m2 and n2 independently represent an integer of 0 to 5;

R^(b9) and R^(b10) independently represent a C₁ to C₃₆ aliphatic hydrocarbon group or a C₃ to C₃₆ alicyclic hydrocarbon group, or R^(b9) and R^(b10) may be bonded together with a sulfur atom bonded thereto to form a sulfur-containing ring, and a methylene group contained in the ring may be replaced by an oxygen atom, sulfur atom or a carbonyl group;

R^(b11) represents a hydrogen atom, a C₁ to C₃₆ aliphatic hydrocarbon group, a C₃ to C₃₆ alicyclic hydrocarbon group or a C₆ to C₁₈ aromatic hydrocarbon group;

R^(b12) represents a C₁ to C₁₂ aliphatic hydrocarbon group, a C₃ to C₁₈ alicyclic hydrocarbon group and a C₆ to C₁₈ aromatic hydrocarbon group, a hydrogen atom contained in an aliphatic hydrocarbon group may be replaced by a C₆ to C₁₈ aromatic hydrocarbon group, and a hydrogen atom contained in an aromatic hydrocarbon group may be replaced by a C₁ to C₁₂ alkoxy group or a C₁ to C₁₂ alkyl carbonyloxy group;

R^(b11) and R^(b12) may be bonded together with —CH—CO— bonded thereto to form a ring, and a methylene group contained in the ring may be replaced by an oxygen atom, sulfur atom or a carbonyl group;

R^(b13), R^(b14), R^(b15), R^(b16), R^(b17) and R^(b18) in each occurrence independently represent a hydroxy group, a C₁ to C₁₂ aliphatic hydrocarbon group or a C₁ to C₁₂ alkoxy group;

L^(b11) represents —S— or —O—;

o2, p2, s2 and t2 independently represent an integer of 0 to 5;

q2 or r2 independently represent an integer of 0 to 4; and

u2 represents an integer of 0 or 1.

Examples of the aliphatic group preferably include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl and 2-ethylhexyl groups. Among these, the aliphatic hydrocarbon group of R^(b9) to R^(b12) is preferably a C₁ to C₁₂ aliphatic hydrocarbon group.

Examples of the alicyclic hydrocarbon group preferably include monocyclic groups such as a cycloalkyl group, i.e., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl groups; and polycyclic hydrocarbon groups such as decahydronaphtyl, adamantyl and norbornyl groups as well as groups below.

Among these, the alicyclic hydrocarbon group of R^(b9) to R^(b12) is preferably a C₃ to C₁₈ alicyclic group, and more preferably a C₄ to C₁₂ alicyclic hydrocarbon group.

Examples of the alicyclic hydrocarbon group where a hydrogen atom may be replaced by an aliphatic hydrocarbon group include methylcyclohexyl, dimethylcyclohexyl, 2-alkyladamantane-2-yl, methylnorbornyl and isobornyl groups. In the alicyclic hydrocarbon group where a hydrogen atom may be replaced by an aliphatic hydrocarbon group, the total carbon number of the alicyclic hydrocarbon group and the aliphatic hydrocarbon group is preferably 20 or less.

Examples of the aromatic hydrocarbon group preferably include an aryl group such as phenyl, tolyl, xylyl, cumenyl, mesityl, p-ethylphenyl, p-tert-butylphenyl, p-cyclohexylphenyl, p-adamantylphenyl, biphenyl, naphthyl, phenanthryl, 2,6-diethylphenyl and 2-methyl-6-ethylphenyl groups.

When the aromatic hydrocarbon includes an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, a C₁ to C₁₈ aliphatic hydrocarbon group or a C₃ to C₁₈ alicyclic hydrocarbon group is preferred.

Examples of the aromatic hydrocarbon group where a hydrogen atom may be replaced by an alkoxy group include a p-methoxyphenyl group.

Examples of the aliphatic hydrocarbon group where a hydrogen atom may be replaced by an aromatic hydrocarbon group include an aralkyl group such as benzyl, phenethyl phenylpropyl, trityl, naphthylmethyl and naphthylethyl groups.

Examples of the alkoxy group include methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, and dodecyloxy groups.

Examples of the acyl group include acetyl, propionyl and butyryl groups.

Examples of the halogen atom include fluorine, chlorine, bromine and iodine atoms.

Examples of the alkylcarbonyloxy group include methylcarbonyloxy, ethylcarbonyloxy, n-propylcarbonyloxy, isopropylcarbonyloxy, n-butylcarbonyloxy, sec-butylcarbonyloxy, tert-butyl carbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy, octylcarbonyloxy and 2-ethylhexylcarobonyloxy groups.

The sulfur atom-containing ring which is formed by R^(b4) and R^(b5) may be a monocyclic or polycyclic one, which may be an aromatic or non-aromatic one, and which may be a saturated or unsaturated one. The ring is preferably a ring having 3 to 18 carbon atoms, and more preferably a ring having 4 to 13 carbon atoms. Examples of the sulfur atom-containing ring include a 3- to 12-membered ring, preferably a 3- to 7-membered ring, examples thereof include rings below.

Examples of the ring formed by R^(b9) and R^(b10) may be any of monocyclic, polycyclic, aromatic, non-aromatic, saturated and unsaturated rings. The ring may be a 3- to 12-membered ring, preferably a 3- to 7-membered ring. Examples of the ring include thiolane-1-ium ring (tetrahydrothiophenium ring), thian-1-ium ring and 1,4-oxathian-4-ium ring.

Examples of the ring formed by R^(b11) and R^(b12) may be of any of monocyclic, polycyclic, aromatic, non-aromatic, saturated and unsaturated rings. The ring may be a 3- to 12-membered ring, preferably a 3- to 7-membered ring. Examples of the ring include oxocycloheptane ring, oxocyclohexane ring, oxonorbornane ring and oxoadamantane ring.

Among the cations represented by formula (b2-1) to formula (b2-4), the cation represented by formula (b2-1) is preferred.

Specific examples of the cation of formula (b2-1) include the following ones.

Specific examples of the cation of the formula (b2-2) include the following ones.

Specific examples of the cation of the formula (b2-3) include the following ones.

The salt (a) includes salts which has any one combination of the above anion and a cation.

Specific examples of the salt (a) include the following ones.

<Method for Producing the Salt (a)>

(1) A method for procuring the salt (a) having an organic cation (Z⁺) and an anion represented by the formula (a2) in which the X¹ is a divalent group represented by the formula (X¹-1), which is represented by formula (I1) and sometimes referred to as “salt (I1)”, is described below.

The salt (I1) can be produced by reacting a salt represented by the formula (I1-a) with a reactant of a compound represented by the formula (I1-b) and carbonyldiimidazole in a solvent:

wherein X^(a), X^(b), L¹, Q¹, Q², the ring W, Z⁺ and R¹ are as defined above.

Preferred examples of the solvent include chloroform and acetonitrile.

Preferred examples of a compound represented by the formula (I1-b) include those represented by the formulae below, which is available on the market.

The salt represented by the formula (I1-a) can be obtained by reacting a salt represented by the formula (I1-c) with a compound represented by the formula (I1-d) in presence of an acidic catalyst in a solvent:

wherein X^(a), X^(b), L¹, Q¹, Q², Z⁺ and the ring W are as defined above.

Preferred examples of an acidic catalyst include p-toluenesulfonic acid,

Preferred examples of the solvent include chloroform, acetonitrile and dimethylformamide.

The salt represented by the formula (I1-c) can be produced according to methods described in JP2007-224008A and JP2012-224611A. Examples the salt include those represented below;

Examples of the compound represented by the formula (I1-d) include one represented by the formula below, which is a marketed product.

(2) A method for procuring the salt (a) having an organic cation (Z⁺) and an anion represented by the formula (a2) in which the X¹ is a divalent group represented by the formula (X¹-4), which salt is represented by the formula (I2) and sometimes referred to as “salt (I2)”, is described below.

The salt (12) can be produced by reacting a salt represented by the formula (I2-a) with a reactant of a compound represented by the formula (I2-b), a compound presented by the formula (I2-b′) and carbonyldiimidazole in a solvent:

wherein X^(a), X^(b), L¹, Q¹, Q², Z⁺, the ring W, R⁵ and R⁶ are as defined above.

Preferred examples of the solvent include chloroform and acetonitrile.

Preferred examples of a compound represented by the formula (I2-b) and a compound represented by the formula (I2-b′) include those represented by the formulae below, which is available on the market.

The salt represented by the formula (I2-a) can be produced by reacting a salt represented by the formula (I2-c) with a compound represented by the formula (I2-d) in presence of an acid catalyst in a solvent:

wherein X^(a), X^(b), L¹, Q¹, Q², Z⁺, the ring W and R¹ are as defined above.

Preferred examples of the acid catalyst include p-toluenesulfonic acid.

Preferred examples of the solvent include chloroform, acetonitrile and dimethylformamide.

The salt represented by the formula (I2-c) can be produced by methods described in JP2007-224008A and JP2012-224611A. Examples of the salt include salts represented below;

A preferred example of a compound represented by the formula (I2-d) includes compound represented by the formula below, which is available on the market.

<Acid Generator>

The salt (a) can function as an active ingredient in an acid generator for a resist composition. An acid generator including the salt (a) is one aspect of the invention. The acid generator may include one or more of the salts (a) together with another salt capable of generating an acid by radiation and so on.

<Resist Composition>

The resist composition has an acid generator having the salt (a) and a resin having an acid-labile group (which is sometimes referred to as “resin (A)”). Here the “acid-labile group” means a group having a leaving group capable of detaching by contacting with an acid to thereby form a hydrophilic group such as a hydroxy or carboxy group.

The resist composition of the present invention may has another acid generator (which is sometimes referred to as “acid generator (B)”) other than the salt (a) as an acid generator.

The resist composition preferably has a quencher (which is sometimes referred to as “quencher (C)”). Further, the resist composition preferably has a solvent (which is sometimes referred to as “solvent (E)”).

Further, the resist composition of the present invention preferably has a salt generating an acid weaker in acidity than an acid generated from the acid generators (which salt is sometimes referred to as “weak acid salt (D)”), examples of which salt include a weak acid inner salt.

<Resin (A)>

The resin (A) includes a structural unit having an acid-labile group (which is sometimes referred to as “structural unit (a1)”). Also, the resin (A) may preferably include a structural unit other than the structural unit (a1). Examples of the structural unit other than the structural unit (a1) includes a structural unit having no acid-labile group (which is sometimes referred to as “structural unit (s)”).

<Structural Unit (a1)>

The structural units (a1) is derived from a monomer (which is sometimes referred to as “monomer (a1)”) having an acid-labile group.

In the resin (A), the acid-labile group contained in the structural unit (a1) is preferably the following one of formula (1) and/or formula (2).

wherein R^(a1) to R^(a3) independently represent a C₁ to C₈ alkyl group, a C₃ to C₂₀ alicyclic hydrocarbon group or combination thereof, or R^(a1) and R^(a2) may be bonded together with a carbon atom bonded thereto to form a C₃ to C₂₀ divalent alicyclic hydrocarbon group;

na represents an integer of 0 or 1;

* represents a binding site.

wherein R^(a1′) and R^(a2′) independently represent a hydrogen atom or a C₁ to C₁₂ hydrocarbon group, R^(a3′) represents a C₁ to C₂₀ hydrocarbon group, or R^(a2′) and R^(a3′) may be bonded together with a carbon atom and X bonded thereto to form a divalent C₃ to C₂₀ heterocyclic group, and a methylene group contained in the hydrocarbon group or the divalent heterocyclic group may be replaced by an oxygen atom or sulfur atom;

X represents —O— or —S—;

* represents a binding site.

Examples of the alkyl group of R^(a1) to R^(a3) include methyl, ethyl, propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group of R^(a1) to R^(a3) include monocyclic groups such as a cycloalkyl group, i.e., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl groups; and polycyclic hydrocarbon groups such as decahydronaphtyl, adamantyl and norbornyl groups as well as groups below. * represents a binding site.

The alicyclic hydrocarbon group of R^(a1) to R^(a3) preferably has 3 to 16 carbon atoms.

Examples of groups combining the alkyl group and the alicyclic hydrocarbon group include methyl cyclohexyl, dimethyl cyclohexyl, methyl norbornyl and cyclohexylmethyl, adamantylmethyl and norbornyletyl groups.

na is preferably an integer of 0.

When R^(a1) and R^(a2) is bonded together to form a divalent alicyclic hydrocarbon group, examples of the group-C(R^(a1))(R^(a2))(R^(a3)) include groups below. The divalent alicyclic hydrocarbon group preferably has 3 to 12 carbon atoms. * represent a binding site to —O—.

Specific examples of the group represented by the formula (1) include, for example,

1,1-dialkylalkoxycarbonyl group (a group in which R^(a1) to R^(a3) are alkyl groups, preferably tert-butoxycarbonyl group, in the formula (1)),

2-alkyladamantane-2-yloxycarbonyl group (a group in which R^(a1), R^(a2) and a carbon atom form adamantyl group, and R^(a3) is alkyl group, in the formula (1)), and

1-(adamantane-1-yl)-1-alkylalkoxycarbonyl group (a group in which R^(a1) and R^(a2) are alkyl group, and R^(a3) is adamantyl group, in the formula (1)).

The hydrocarbon group of R^(a1′) to R^(a3′) includes any of an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a group formed by combining them.

Examples of the alkyl group and the alicyclic hydrocarbon group are the same examples as described above.

Examples of the aromatic hydrocarbon group include an aryl group such as phenyl, naphthyl, anthryl, p-methylphenyl, p-tert-butylphenyl, p-adamantylphenyl, tolyl, xylyl, cumenyl, mesityl, biphenyl, phenanthryl, 2,6-diethylphenyl and 2-methyl-6-ethylphenyl groups.

Examples of the divalent heterocyclic group formed by bonding with R^(a2′) and R^(a3′) include groups below.

At least one of R^(a1′) and R^(a2′) is preferably a hydrogen atom.

Specific examples of the group represented by the formula (2) include a group below. * represents a binding site.

The monomer (a1) is preferably a monomer having an acid-labile group and an ethylene unsaturated bond, and more preferably a (meth)acrylic monomer having the acid-labile group.

Among the (meth)acrylic monomer having an acid-labile group, a monomer having a C₅ to C₂₀ alicyclic hydrocarbon group is preferred. When a resin (A) having a structural unit derived from a monomer (a1) having a bulky structure such as the alicyclic hydrocarbon group is used for a resist composition, the resist composition having excellent resolution tends to be obtained.

Examples of a structural unit derived from the (meth)acrylic monomer having the group represented by the formula (1) preferably include structural units represented by the formula (a1-0), the formula (a1-1) and the formula (a1-2) below. These may be used as a single structural unit or as a combination of two or more structural units. The structural unit represented by the formula (a1-0), the structural unit represented by the formula (a1-1) and a structural unit represented by the formula (a1-2) are sometimes referred to as “structural unit (a1-0)”, “structural unit (a1-1)” and “structural unit (a1-2)”), respectively, and monomers deriving the structural unit (a1-0), the structural unit (a1-1) and the structural unit (a1-2) are sometimes referred to as “monomer (a1-0)”, “monomer (a1-1)” and “monomer (a1-2)”), respectively:

wherein L^(a01) represents —O— or *—O—(CH₂)_(k01)—CO—O—,

k01 represents an integer of 1 to 7,

* represents a binding site to —CO—,

R^(a01) represents a hydrogen atom or a methyl group, and

R^(a02), R^(a03) and R^(a04) independently represent a C₁ to C₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or combination thereof.

L^(a01) is preferably an —O— or *—O—(CH₂)_(k01)—CO—O— in which k01 is preferably an integer of 1 to 4, more preferably an integer of 1, more preferably an —O—.

Examples of the alkyl group and an alicyclic hydrocarbon group of R^(a02), R^(a03) and R^(a04) and combination thereof are the same examples as the group described in R^(a1) to R^(a3) in the formula (1).

The alkyl group of R^(a02), R^(a03) and R^(a04) is preferably a C₁ to C₆ alkyl group.

The alicyclic hydrocarbon group of R^(a02), R^(a03) and R^(a04) is preferably a C₃ to C₈ alicyclic hydrocarbon group, more preferably a C₃ to C₆ alicyclic hydrocarbon group.

The group formed by combining the alkyl group and the alicyclic hydrocarbon group has preferably 18 or less of carbon atom. Examples of those groups include methyl cyclohexyl, dimethyl cyclohexyl and methyl norbornyl groups.

R^(a02) and R^(a03) is preferably a C₁ to C₆ alkyl group, more preferably a methyl or ethyl group.

R^(a04) is preferably a C₁ to C₆ alkyl group or C₅ to C₁₂ alicyclic hydrocarbon group, more preferably a methyl, ethyl, cyclohexyl or adamantyl group.

wherein L^(a1) and L^(a2) independently represent —O— or *—O—(CH₂)_(k1)—CO—O—,

k1 represents an integer of 1 to 7,

* represents a binding site to —CO—,

R^(a4) and R^(a5) independently represent a hydrogen atom or a methyl group,

R^(a6) and R^(a7) independently represent a C₁ to C₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or a combination thereof,

m1 represents an integer of 0 to 14,

n1 represents an integer of 0 to 10, and

n1′ represents an integer of 0 to 3.

L^(a1) and L^(a2) are preferably —O— or *—O—(CH₂)_(k1′)—CO—O— in which k1′ represents an integer of 1 to 4 and more preferably 1, still more preferably —O—.

R^(a4) and R^(a5) are preferably a methyl group.

Examples of the alkyl group of R^(a6) and R^(a7) include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group of R^(a6) and R^(a7) include monocyclic hydrocarbon groups such as a cycloalkyl group, i.e., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, cycloheptyl and cyclooctyl groups; and polycyclic hydrocarbon groups such as decahydronaphtyl, adamantyl, 2-alkyadamantane-2-yl, 1-(adamantane-1-yl) alkane-1-yl, norbornyl, methyl norbornyl and isobornyl groups.

Examples of group formed by combining the alkyl group and the alicyclic hydrocarbon group of R^(a6) and R^(a7) include an aralkyl group such as benzyl and phenethyl groups.

The alkyl group of R^(a6) and R^(a7) is preferably a C₁ to C₆ alkyl group.

The alicyclic hydrocarbon group of R^(a6) and R^(a7) is preferably a C₃ to C₈ alicyclic hydrocarbon group, more preferably a C₃ to C₆ alicyclic hydrocarbon group.

m1 is preferably an integer of 0 to 3, and more preferably 0 or 1.

n1 is preferably an integer of 0 to 3, and more preferably 0 or 1.

n1′ is preferably 0 or 1, and more preferably 1.

Examples of the monomer (a1-0) preferably include monomers represented by the formula (a1-0-1) to the formula (a1-0-12), and more preferably monomers represented by the formula (a1-0-1) to the formula (a1-0-10) below.

Examples of the structural units (a1-0) include structural units in which a methyl group corresponding to R^(a01) in the structural units represented as above has been replaced by a hydrogen atom.

Examples of the monomer (a1-1) include monomers described in JP 2010-204646A. Among these, the monomers are preferably monomers represented by the formula (a1-1-1) to the formula (a1-1-8), and more preferably monomers represented by the formula (a1-1-1) to the formula (a1-1-4) below.

Examples of the monomer (a1-2) include 1-methylcyclopentane-1-yl(meth)acrylate, 1-ethylcyclopentane-1-yl (meth)acrylate, 1-methylcyclohexane-1-yl (meth)acrylate, 1-ethylcyclohexane-1-yl (meth)acrylate, 1-ethylcycloheptane-1-yl (meth)acrylate, 1-ethylcyclooctane-1-yl (meth)acrylate, 1-isopropylcyclopentane-1-yl (meth)acrylate and 1-isopropylcyclohexane-1-yl(meth)acrylate. Among these, the monomers are preferably monomers represented by the formula (a1-2-1) to the formula (a1-2-12), and more preferably monomers represented by the formula (a1-2-3), the formula (a1-2-4), the formula (a1-2-9) and the formula (a1-2-10), and still more preferably monomer represented by the formula (a1-2-3) and the formula (a1-2-9) below.

When the resin (A) contains the structural unit (a1-0) and/or the structural unit (a1-1) and/or the structural unit (a1-2), the total proportion thereof is generally 10 to 95% by mole, preferably 15 to 90% by mole, more preferably 20 to 85% by mole, with respect to the total structural units (100% by mole) of the resin (A).

Further, examples of the structural unit (a1) having a group (1) include a structural unit presented by the formula (a1-3). The structural unit represented by the formula (a1-3) is sometimes referred to as “structural unit (a1-3)”. The monomer from which the structural unit (a1-3) is derived is sometimes referred to as “monomer (a1-3)”.

wherein R^(a9) represents a carboxy group, a cyano group, a —COOR^(a13), a hydrogen atom or a C₁ to C₃ aliphatic hydrocarbon group that may have a hydroxy group,

R^(a13) represents a C₁ to C₈ aliphatic hydrocarbon group, a C₃ to C₂₀ alicyclic hydrocarbon group or a group formed by combining thereof, a hydrogen atom contained in the aliphatic hydrocarbon group and the alicyclic hydrocarbon group may be replaced by a hydroxy group, a methylene group contained in the aliphatic hydrocarbon group and the alicyclic hydrocarbon group may be replaced by an oxygen atom or a carbonyl group, and

R^(a10), R^(a11) and R^(a12) independently represent a C₁ to C₈ alkyl hydrocarbon group, a C₃ to C₂₀ alicyclic hydrocarbon group or a group formed by combining them, or R^(a10) and R^(a11) may be bonded together with a carbon atom bonded thereto to form a C₁ to C₂₀ divalent hydrocarbon group.

Here, examples of —COOR^(a13) group include a group in which a carbonyl group is bonds to the alkoxy group, such as methoxycarbonyl and ethoxycarbonyl groups.

Examples of the aliphatic hydrocarbon group that may have a hydroxy group of R^(a9) include methyl, ethyl, propyl, hydroxymethyl and 2-hydroxyethyl groups.

Examples of the C₁ to C₈ aliphatic hydrocarbon group of R^(a13) include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the C₃ to C₂₀ alicyclic hydrocarbon group of R^(a13) include cyclopentyl, cyclopropyl, adamantyl, adamantylmetyl, 1-(adamantyl-1-yl)-methylethyl, 2-oxo-oxolane-3-yl, 2-oxo-oxolane-4-yl groups.

Examples of the alkyl group of R^(a10) to R^(a12) include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group of R^(a10) to R^(a12) include monocyclic hydrocarbon groups such as a cycloalkyl group, i.e., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, cyclooctyl, cycloheptyl and cyclodecyl groups; and polycyclic hydrocarbon groups such as decahydronaphtyl, adamantyl, 2-alkyl-2-adamantyl, 1-(adamantane-1-yl) alkane-1-yl, norbornyl, methyl norbornyl and isobornyl groups.

When R^(a10) and R^(a11) is bonded together with a carbon atom bonded thereto to form a divalent hydrocarbon group, examples of the group-C(R^(a10))(R^(a11))(R^(a12)) include groups below.

Examples of the monomer (a1-3) include tert-butyl 5-norbornene-2-carboxylate, 1-cyclohexyl-1-methylethyl 5-norbornene-2-carboxylate, 1-methylcyclohexyl 5-norbornene-2-carboxylate, 2-methy-2-adamantane-2-yl 5-norbornene-2-carboxylate, 2-ethyl-2-adamantane-2-yl 5-norbornene-2-carboxylate, 1-(4-methycyclohexyl)-1-methylethyl 5-norbornene-2-carboxylate, 1-(4-hydroxycyclohexyl)-1-methylethyl 5-norbornene-2-carboxylate, 1-methyl-(4-oxocyclohexyl)-1-ethyl 5-norbornene-2-carboxylate, and 1-(1-adamantane-1-yl)-1-methylethyl 5-norbornene-2-carboxylate.

The resin (A) having a structural unit (a1-3) can improve the resolution of the obtained resist composition because it has a bulky structure, and also can improve a dry-etching tolerance of the obtained resist composition because of incorporated a rigid norbornene ring into a main chain of the resin (A).

When the resin (A) contains the structural unit (a1-3), the proportion thereof is generally 10% by mole to 95% by mole, preferably 15% by mole to 90% by mole, and more preferably 20% by mole to 85% by mole, with respect to the total structural units constituting the resin (A) (100% by mole).

Examples of a structural unit (a1) having a group (2) include a structural unit represented by the formula (a1-4). The structural unit is sometimes referred to as “structural unit (a1-4)”.

wherein R^(a32) represents a hydrogen atom, a halogen atom or a C₁ to C₆ alkyl group that may have a halogen atom,

R^(a33) in each occurrence independently represent a halogen atom, a hydroxy group, a C₁ to C₆ alkyl group, a C₁ to C₆ alkoxy group, a C₂ to C₄ acyl group, a C₂ to C₄ acyloxy group, an acryloyloxy group or methacryloyloxy group,

la represents an integer 0 to 4,

R^(a34) and R^(a35) independently represent a hydrogen atom or a C₁ to C₁₂ hydrocarbon group; and

R^(a36) represents a C₁ to C₂₀ hydrocarbon group, or R^(a35) and R^(a36) may be bonded together with a C—O bonded thereto to form a divalent C₂ to C₂₀ hydrocarbon group, and a methylene group contained in the hydrocarbon group or the divalent hydrocarbon group may be replaced by an oxygen atom or sulfur atom.

Examples of the alkyl group of R^(a32) and R^(a33) include methyl, ethyl, propyl, isopropyl, butyl, pentyl and hexyl groups. The alkyl group is preferably a C₁ to C₄ alkyl group, and more preferably a methyl or ethyl group, and still more preferably a methyl group.

Examples of the halogen atom of R^(a32) and R^(a33) include fluorine, chlorine, bromine or iodine atom.

Examples of the alkyl group that may have a halogen atom include trifluoromethyl, difluoromethyl, methyl, perfluoromethyl, 1,1,1-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, ethyl, perfluoropropyl, 1,1,1,2,2-pentafluoropropyl, propyl, perfluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, butyl, perfluoropentyl, 1,1,1,2,2,3,3,4,4-nonafluoropentyl, n-pentyl, n-hexyl and n-perfluorohexyl groups.

Examples of an alkoxy group include methoxy, ethoxy, propoxy, butoxy, pentyloxy, and hexyloxy groups. The alkoxy group is preferably a C₁ to C₄ alkoxy group, more preferably a methoxy and ethoxy group, and still more preferably methoxy group.

Examples of the acyl group include acetyl, propanonyl and butylyl groups.

Examples of the acyloxy group include acetyloxy, propanonyloxy and butylyloxy groups.

Examples of the hydrocarbon group of R^(a34) and R^(a35) are the same examples as described in R^(a1′) to R^(a2′) in the formula (2).

Examples of hydrocarbon group of R^(a36) include a C₁ to C₁₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group, a C₆ to C₁₈ aromatic hydrocarbon group or a group formed by combining them.

In the formula (a1-4), R^(a32) is preferably a hydrogen atom.

R^(a33) is preferably a C₁ to C₄ alkoxy group, more preferably a methoxy and ethoxy groups, and still more preferably methoxy group.

la is preferably 0 or 1, and more preferably 0.

R^(a34) is preferably a hydrogen atom.

R^(a35) is preferably a C₁ to C₁₂ hydrocarbon group, and more preferably a methyl or ethyl group.

The hydrocarbon group of R^(a36) is preferably a C₁ to C₁₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group, a C₆ to C₁₈ aromatic hydrocarbon group or a combination thereof, and more preferably a C₁ to C₁₈ alkyl group, a C₃ to C₁₈ alicyclic hydrocarbon group or a C₇ to C₁₈ aralkyl group. The alkyl group and the alicyclic hydrocarbon group of R^(a36) is preferably not substituted. When the aromatic hydrocarbon group of R^(a36) has a substituent, the substituent is preferably a C₆ to C₁₀ aryloxy group.

Examples of the monomer from which a structural unit (a1-4) is derived include monomers described in JP 2010-204646A. Among these, the monomers are preferably monomers represented by the formula (a1-4-1) to the formula (a1-4-7), and more preferably monomers represented by the formula (a1-4-1) to the formula (a1-4-5) below.

When the resin (A) contains the structural unit (a1-4), the proportion thereof is generally 10% by mole to 95% by mole, preferably 15% by mole to 90% by mole, more preferably 20% by mole to 85% by mole, with respect to the total structural units constituting the resin (A) (100% by mole).

Examples of a structural unit having an acid-labile group include a structural unit represented by the formula (a1-5). Such structural unit is sometimes referred to as “structural unit (a1-5)”.

wherein R^(a8) represents a hydrogen atom, a halogen atom or a C₁ to C₆ alkyl group that may have a halogen atom,

Z^(a1) represent a single bond or *—(CH₂)_(h3)—CO-L⁵⁴-,

h3 represents an integer of 1 to 4,

* represents a binding site to L⁵¹,

L⁵¹, L⁵² and L⁵³ independently represent —O— or —S—,

s1 represents an integer of 1 to 3, and

s1′ represents an integer of 0 to 3.

In the formula (a1-5), R^(a8) is preferably a hydrogen atom, a methyl group or trifluoromethyl group;

L⁵¹ is preferably —O—;

L⁵² and L⁵³ are independently preferably —O— or —S—, and more preferably one is —O— and another is —S—.

s1 is preferably 1;

s1′ is preferably an integer of 0 to 2;

Z^(a1) is preferably a single bond or *—CH₂—CO—O—.

Examples of a monomer from which a structural unit (a1-5) is derived include a monomer described in JP 2010-61117A. Among these, the monomers are preferably monomers represented by the formula (a1-5-1) to the formula (a1-5-4), and more preferably monomers represented by the formula (a1-5-1) to the formula (a1-5-2) below.

When the resin (A) contains the structural unit (a1-5), the proportion thereof is generally 1% by mole to 50% by mole, preferably 3% by mole to 45% by mole, and more preferably 5% by mole to 40% by mole, with respect to the total structural units (100% by mole) constituting the resin (A).

Examples of a structural unit (a1) having an acid-labile group in a resin (A) is preferably at least one, more preferably two or more structural units selected from the structural unit (a1-0), the structural unit (a1-1), the structural unit (a1-2), the structural unit (a1-5), still more preferably a combination of the structural unit (a1-1) and the structural unit (a1-2), a combination of the structural unit (a1-1) and the structural unit (a1-5), a combination of the structural unit (a1-1) and the structural unit (a1-0), a combination of the structural unit (a1-2) and the structural unit (a1-0), a combination of the structural unit (a1-5) and the structural unit (a1-0), a combination of the structural unit (a1-0), the structural unit (a1-1) and the structural unit (a1-2), a combination of the structural unit (a1-0), the structural unit (a1-1) and the structural unit (a1-5), in particular preferably a combination of the structural unit (a1-1) and the structural unit (a1-2), and a combination of the structural unit (a1-1) and the structural unit (a1-5).

<Structural Unit Having No Acid-Labile Group (s)>

The structural units (s) is derived from a monomer (which is sometimes referred to as “monomer (s)”) having no acid-labile group.

For the monomer (s) from which a structural unit (s) is derived, a known monomer having no acid-labile group can be used.

As the structural unit (s), a structural unit having a hydroxy group or a lactone ring but having no acid-labile group is preferred. When a resin containing the structural unit derived from a structural unit having hydroxy group but having no acid-labile group (such structural unit is sometimes referred to as “structural unit (a2)”) and/or a structural unit having a lactone ring but having no acid-labile group (such structural unit is sometimes referred to as “structural unit (a3)”) is used, the adhesiveness of resist to a substrate and resolution of resist pattern tend to be improved.

<Structural Unit (a2)>

The structural unit (a2) having a hydroxy group may be an alcoholic hydroxy group or a phenolic hydroxy group.

When KrF excimer laser lithography (248 nm), or high-energy irradiation such as electron beam or EUV (extreme ultraviolet) is used for the resist composition, using the structural unit having a phenolic hydroxy group as structural unit (a2) is preferred.

When ArF excimer laser lithography (193 nm) is used, using the structural unit having an alcoholic hydroxy group as the structural unit (a2) is preferred, using the structural represented by the formula (a2-1) is more preferred.

The structural unit (a2) may be used as a single structural unit or as a combination of two or more structural units.

Examples of the structural unit (a2) having a phenolic hydroxy group include the structural unit (which is sometimes referred to as “structural unit (a2-0)”) represented by the formula (a2-0).

wherein R^(a30) represents a hydrogen atom, a halogen atom or a C₁ to C₆ alkyl group that may have a halogen atom,

R^(a31) in each occurrence independently represents a halogen atom, a hydroxy group, a C₁ to C₆ alkyl group, a C₁ to C₆ alkoxy group, a C₂ to C₄ acyl group, a C₂ to C₄ acyloxy group, an acryloyloxy group or methacryloyloxy group, and

ma represents an integer 0 to 4.

Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, n-pentyl and n-hexyl groups.

Example of the halogen atom is a chlorine atom, a fluorine atom and bromine atom.

Examples of a C₁ to C₆ alkyl group that may have a halogen atom of R^(a30) include trifluoromethyl, difluoromethyl, methyl, perfluoromethyl, 1,1,1-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, ethyl, perfluoropropyl, 1,1,1,2,2-pentafluoropropyl, propyl, perfluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, butyl, perfluoropentyl, 1,1,1,2,2,3,3,4,4-nonafluoropentyl, n-pentyl, n-hexyl and n-perfluorohexyl groups.

R^(a30) is preferably a hydrogen atom or a C₁ to C₄ alkyl group, and more preferably a hydrogen atom, methyl or ethyl group, and still more preferably a hydrogen atom or methyl group.

Examples of a C₁ to C₆ alkoxy group of R^(a31) include methoxy, ethoxy, propoxy, butoxy, pentyloxy, and hexyloxy groups. R^(a31) is preferably a C₁ to C₄ alkoxy group, more preferably a methoxy and ethoxy group, and still more preferably methoxy group.

Examples of the acyl group include acetyl, propanonyl and butylyl groups.

Examples of the acyloxy group include acetyloxy, propanonyloxy and butylyloxy groups.

ma is preferably 0, 1 or 2, more preferably 0 or 1, still more preferably 0.

The structural unit (a2-0) having a phenolic hydroxy group is preferably a structural unit represented below.

Among these, a structural unit represented by the formula (a2-O-1) or the formula (a2-O-2) is preferred.

Examples of a monomer from which the structural unit (a2-0) is derived include monomers described in JP2010-204634A.

The resin (A) which contains the structural units (a2) having a phenolic hydroxy group can be produced, for example, by polymerizing a monomer where its phenolic hydroxy group has been protected with a suitable protecting group, followed by deprotection. The deprotection is carried in such a manner that an acid-labile group in the structural unit (a1) is significantly impaired. Examples of the protecting group for a phenolic hydroxy group include an acetyl group.

When the resin (A) contains the structural unit (a2-0) having the phenolic hydroxy group, the proportion thereof is generally 5% by mole to 95% by mole, preferably 10% by mole to 80% by mole, more preferably 15% by mole to 80% by mole, with respect to the total structural units (100% by mole) constituting the resin (A).

Examples of the structural unit (a2) having alcoholic hydroxy group include the structural unit (which is sometimes referred to as “structural unit (a2-1)”) represented by the formula (a2-1).

wherein L^(a3) represents —O— or *—O—(CH₂)_(k2)—CO—O—,

k2 represents an integer of 1 to 7,

* represents a binding site to —CO—,

R^(a14) represents a hydrogen atom or a methyl group,

R^(a15) and R^(a16) each independently represent a hydrogen atom, a methyl group or a hydroxy group, and

o1 represents an integer of 0 to 10.

In the formula (a2-1), L^(a3) is preferably —O—, —O—(CH₂)_(f1)—CO—O—, here f1 represents an integer of 1 to 4, and more preferably —O—.

R^(a14) is preferably a methyl group.

R^(a15) is preferably a hydrogen atom.

R^(a16) is preferably a hydrogen atom or a hydroxy group.

o1 is preferably an integer of 0 to 3, and more preferably an integer of 0 or 1.

Examples of the monomer from which the structural unit (a2-1) is derived include monomers described in JP 2010-204646A. Among these, the monomers are preferably monomers represented by the formula (a2-1-1) to the formula (a2-1-6), more preferably structural units represented by the formula (a2-1-1) to the formula (a2-1-4), and still more preferably structural units represented by the formula (a2-1-1) and the formula (a2-1-3) below.

Examples of monomers introducing the structural unit (a2) having the alcoholic hydroxy group include monomers described in JP 2010-204646A.

When the resin (A) contains the structural unit (a2) having the alcoholic hydroxy group, the proportion thereof is generally 1% by mole to 45% by mole, preferably 1% by mole to 40% by mole, more preferably 1% by mole to 35% by mole, and still more preferably 2% by mole to 20% by mole, with respect to the total structural units (100% by mole) constituting the resin (A).

<Structural Unit (a3)>

The lactone ring included in the structural unit (a3) may be a monocyclic compound such as β-propiolactone, γ-butyrolactone, δ-valerolactone, or a condensed ring of monocyclic lactone ring with another ring. Examples of the lactone ring preferably include γ-butyrolactone, amadantane lactone, or bridged ring with γ-butyrolactone.

Examples of the structural unit (a3) include structural units represented by any of the formula (a3-1), the formula (a3-2), the formula (a3-3) and the formula (a3-4). These structural units may be used as a single unit or as a combination of two or more units.

wherein L^(a4) represents *—O— or *—O—(CH₂)_(k3)—CO—O—, k3 represents an integer of 1 to 7, * represents a binding site to a carbonyl group,

R^(a18) represents a hydrogen atom or a methyl group,

R^(a21) in each occurrence represents a C₁ to C₄ aliphatic hydrocarbon group, and

p1 represents an integer of 0 to 5,

L^(a5) represents *—O— or *—O—(CH₂)_(k3)—CO—O—, k3 represents an integer of 1 to 7, * represents a binding site to a carbonyl group,

-   -   R^(a19) represents a hydrogen atom or a methyl group,

R^(a22) in each occurrence represents a carboxy group, a cyano group or a C₁ to C₄ aliphatic hydrocarbon group,

q1 represents an integer of 0 to 3,

L^(a6) represents *—O— or *—O—(CH₂)_(k3)—CO—O—, k3 represents an integer of 1 to 7, * represents a binding site to a carbonyl group,

R^(a20) represents a hydrogen atom or a methyl group,

R^(a23) in each occurrence represents a carboxy group, a cyano group or a C₁ to C₄ aliphatic hydrocarbon group, and

r1 represents an integer of 0 to 3,

R^(a24) represents a hydrogen atom, a halogen atom or a C₁ to C₆ alkyl group that may have a halogen atom,

L^(a7) represents a single bond, *-L^(a8)-O—, -L^(a8)-CO—O—, *-L^(a8)-CO—O-L^(a9)-CO—O—, or *-L^(a8)-O—CO-L^(a9)-O—; * represents a binding site to a carbonyl group, and

L^(a8) and L^(a9) independently represents a C₁ to C₆ alkanediyl group.

Examples of the aliphatic hydrocarbon group R^(a21), R^(a22) and R^(a23) include an alkyl group such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and tert-butyl groups.

Examples of the halogen atom of R^(a24) include fluorine, chlorine, bromine or iodine atom;

Examples of the alkyl group of R^(a24) include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl and n-hexyl groups, preferably a C₁ to C₄ alkyl group, more preferably a methyl or ethyl group.

Examples of the alkyl group having a halogen atom of R^(a24) include trifluoromethyl, perfluoroethyl, perfluoropropyl, perfluoro-isopropyl, perfluorobutyl, perfluoro-sec-butyl, perfluoro-tert-butyl, perfluoropentyl, perfluorohexyl, trichloromethyl, tribromomethyl and triiodomethyl groups.

Examples of the alkanediyl group of L^(a8) and L^(a9) include methylene, ethylene, propane-1,3-diyl, propane-1,2-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, butane-1,3-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl and 2-methylbutane-1,4-diyl groups.

In the formulae (a3-1) to (a3-3), L^(a4) to L^(a6) is independently preferably —O—, *—O—(CH₂)_(k3′)—CO—O—, here k3′ represents an integer of 1 to 4, more preferably —O— or *—O—CH₂—CO—O—, and still more preferably *—O—.

R^(a18) to R^(a21) is preferably a methyl group.

R^(a22) and R^(a23) are independently preferably a carboxy group, a cyano group or a methyl group.

p1, q1 and r1 are independently preferably an integer of 0 to 2, and more preferably 0 or 1.

In the formula (a3-4), R^(a24) is preferably a hydrogen atom or a C₁ to C₄ alkyl group, more preferably a hydrogen atom, a methyl group or an ethyl group, and still more preferably a hydrogen atom or a methyl group.

L^(a7) is preferably a single bond or *-L^(a8)-CO—O—, and more preferably a single bond, —CH₂—CO—O— or —C₂H₄—CO—O—.

Examples of the monomer from which the structural unit (a3) is derived include monomers described in JP 2010-204646A, monomers described in JP2000-122294A and monomers described in JP2012-41274A. Among these, the structural units are preferably structural units represented by the formula (a3-1-1) to the formula (a3-1-4), the formula (a3-2-1) to the formula (a3-2-4), the formula (a3-3-1) to the formula (a3-3-4), the formula (a3-4-1) to the formula (a3-4-12), more preferably monomers represented by the formula (a3-1-1) to the formula (a3-1-2), the formula (a3-2-3), the formula (a3-2-4), the formula (a3-4-1) and the formula (a3-4-2), and still more preferably monomers represented by the formula (a3-1-1), the formula (a3-2-3) or the formula (a3-4-2) below.

When the resin (A) contains the structural units (a3), the total proportion thereof is preferably 5% by mole to 70% by mole, more preferably 10% by mole to 65% by mole, still more preferably 10% by mole to 60% by mole, with respect to the total structural units (100% by mole) constituting the resin (A).

The proportion each of the formula (a3-1), the formula (a3-2), the formula (a3-3) and the formula (a3-4) is preferably 5% by mole to 60% by mole, more preferably 5% by mole to 50% by mole, still more preferably 10% by mole to 50% by mole, with respect to the total structural units (100% by mole) constituting the resin (A).

<Other Structural Unit (t)>

The resin (A) may include a structural unit other than the structural unit (a1) and the structural unit (s) described above (which is sometimes referred to as “structural unit (t)”). Examples of the structural unit (t) include a structural unit having a halogen atom (which is sometimes referred to as “structural unit (a4)”) other than the structural unit (a1) and the structural unit (a3), and a structural unit having a non-leaving hydrocarbon group (which is sometimes referred to as “structural unit (a5)”).

<Structural Unit (a4)>

The structural unit having a halogen atom preferably has a fluorine atom.

Examples of the structural unit (a4) include the structural units represented by the formula (a4-0).

wherein R⁵ represents a hydrogen atom or a methyl group,

L⁵ represent a single bond or a C₁ to C₄ saturated aliphatic hydrocarbon group,

L³ represents a C₁ to C₈ perfluoroalkanediyl group or a C₅ to C₁₂ perfluorocycloalkanediyl group, and

R⁶ represents a hydrogen atom or a fluorine atom.

Examples of the saturated aliphatic hydrocarbon group of L⁵ include a liner alkanediyl group such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl; and a branched alkanediyl group such as a group in which a liner alkanediyl group has a side chain of an alkyl group (e.g., methyl and ethyl groups), for example, ethane-1,1-diyl, propane-1,2-diyl, butane-1,3-diyl, 2-methylpropane-1,3-diyl and 2-methylpropane-1,2-diyl groups.

Examples of the perfluoroalkanediyl group of L³ include difluoromethylene, perfluoroethylene, perfluoroethyl fluoromethylene, perfluoropropane-1,3-diyl, a perfluoropropane-1,2-diyl, perfluoropropane-2,2-diyl, perfluorobutane-1,4-diyl, perfluorobutane-2,2-diyl, perfluorobutane-1,2-diyl, perfluoropentane-1,5-diyl, perfluoropentane-2,2-diyl, perfluoropentane-3,3-diyl, perfluorohexane-1,6-diyl, perfluorohexane-2,2-diyl, perfluorohexane-3,3-diyl, perfluoroheptane-1,7-diyl, perfluoroheptane-2,2-diyl, perfluoroheptane-3,4-diyl, perfluoroheptane-4,4-diyl, perfluorooctan-1,8-diyl, perfluorooctan-2,2-diyl, perfluorooctan-3,3-diyl and perfluorooctan-4,4-diyl groups.

Examples of the perfluoro cycloalkanediyl group of L³ include perfluorocyclohexanediyl, perfluorocyclopentanadiyl, perfluorocycloheptanediyl and perfluoroadamantanediyl groups.

L⁵ is preferably a single bond, methylene or ethylene group, and more preferably a single bond or methylene group.

L³ is preferably a C₁ to C₆ perfluoroalkanediyl group, more preferably a C₁ to C₃ perfluoroalkanediyl group.

Examples of the structural unit (a4-0) include structural units represented by the formula (a4-0-1) to the formula (a4-0-32).

Examples of the structural unit (a4) include the structural units represented by the formula (a4-1):

wherein R^(a41) represents a hydrogen atom or a methyl group,

R^(a42) represents an optionally substituted C₁ to C₂₀ hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and

A^(a41) represents an optionally substituted C₁ to C₆ alkanediyl group or a group represented by the formula (a-g1),

wherein s represents 0 or 1,

A^(a42) and A^(a44) independently represent an optionally substituted C₁ to C₅ aliphatic hydrocarbon group,

A^(a43) represents a single bond or an optionally substituted C₁ to C₅ aliphatic hydrocarbon group, and

X^(a41) and X^(a42) independently represent —O—, —CO—, —CO—O— or —O—CO—, provided that the total carbon number contained in the group of A^(a42), A^(a43), A^(a44), X^(a41) and X^(a42) is 6 or less, and

at least one of A^(a41) and R^(a42) has a halogen atom as a substituent, and

* and ** represent a binding site, and * represents a binding site to —O—CO—R^(a42).

The hydrocarbon group of R^(a42) includes a chain and a cyclic aliphatic hydrocarbon groups, an aromatic hydrocarbon group and a combination thereof.

Examples of the chain aliphatic hydrocarbon group include an alkyl group such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl and n-octadecyl groups. Examples of the cyclic aliphatic hydrocarbon group include a monocyclic hydrocarbon group, i.e., cycloalkyl group such as cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl groups; and polycyclic hydrocarbon groups such as decahydronaphtyl, adamantyl and norbornyl groups as well as groups below. * represents a binding site.

Examples of the aromatic hydrocarbon group include an aryl group such as phenyl, naphthyl, anthryl, biphenyl, phenanthryl and fluorenyl groups.

The hydrocarbon group of R^(a42) is preferably a chain and a cyclic aliphatic hydrocarbon groups, and a combination thereof. The hydrocarbon group may have a carbon-carbon unsaturated bond, is preferably a chain and a cyclic saturated aliphatic hydrocarbon groups, and a combination thereof

Examples of the substituent of R^(a42) include a fluorine atom or a group represented by the formula (a-g3).

Examples of the halogen atom include fluorine, chlorine, bromine or iodine atom, and preferably a fluorine atom. *—X^(a43)-A^(a45)  (a-g3) wherein X^(a43) represent an oxygen atom, a carbonyl group, a carbonyloxy group or an oxycarbonyl group,

A^(a45) represents a C₁ to C₁₇ aliphatic hydrocarbon group that has a halogen atom, and

* represents a binding site to carbonyl group.

Examples of the aliphatic hydrocarbon group of A^(a45) are the same examples as the group of R^(a42).

R^(a42) is preferably an aliphatic hydrocarbon group that may have a halogen atom, and more preferably an alkyl group having a halogen atom and/or an aliphatic hydrocarbon group having the group represented by the formula (a-g3).

When R^(a42) is an aliphatic hydrocarbon group having a halogen atom, an aliphatic hydrocarbon group having a fluorine atom is preferred, a perfluoroalkyl group or a perfluorocycloalkyl group are more preferred, a C₁ to C₆ perfluoroalkyl group is still more preferred, a C₁ to C₃ perfluoroalkyl group is particularly preferred.

Examples of the perfluoroalkyl group include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, perfluorohexyl, perfluoroheptyl and perfluorooctyl groups. Examples of the perfluorocycloalkyl group include perfluorocyclohexyl group.

When R^(a42) is an aliphatic hydrocarbon group having the group represented by the formula (a-g3), the total carbon number contained in the aliphatic hydrocarbon group including the group represented by the formula (a-g3) is preferably 15 or less, more preferably 12 or less. The number of the group represented by the formula (a-g3) is preferably one when the group represented by the formula (a-g3) is the substituent.

The aliphatic hydrocarbon having the group represented by the formula (a-g3) is more preferably a group represented by the formula (a-g2); *-A^(a46)-X^(a44)-A^(a47)  (a-g2)

wherein A^(a46) represents a C₁ to C₁₇ aliphatic hydrocarbon group that may have a halogen atom,

X^(a44) represent a carbonyloxy group or an oxycarbonyl group,

A^(a47) represents a C₁ to C₁₇ aliphatic hydrocarbon group that may have a halogen atom, provided that the total carbon number contained in the group of A^(a46), X^(a44) and A^(a47) is 18 or less,

at least one of A^(a46) and A^(a47) has a halogen atom, and

* represents a binding site to carbonyl group.

The carbon number of the aliphatic hydrocarbon group of A^(a46) is preferably 1 to 6, and more preferably 1 to 3.

The carbon number of the aliphatic hydrocarbon group of A^(a47) is preferably 4 to 15, and more preferably 5 to 12, and cyclohexyl and adamantyl groups are still more preferred as the aliphatic hydrocarbon group.

Preferred structure represented by the formula (a-g2), *-A^(a46)-X^(a44)-A^(a47) include the following ones.

Examples of the alkanediyl group of A^(a41) include a liner alkanediyl group such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl and hexane-1,6-diyl groups;

a branched alkanediyl group such as propane-1,2-diyl, butan-1,3-diyl, 2-methylpropane-1,2-diyl, 1-methylpropane-1,4-diyl, 2-methylbutane-1,4-diyl groups.

Examples of the substituent of the alkanediyl group of A^(a41) include a hydroxy group and a C₁ to C₆ alkoxy group.

A^(a41) is preferably a C₁ to C₄ alkanediyl group, more preferably a C₂ to C₄ alkanediyl group, and still more preferably ethylene group.

In the group represented by the formula (a-g1) (which is sometimes referred to as “group (a-g1)”), examples of the aliphatic hydrocarbon group of A^(a42), A^(a43) and A^(a44) include methylene, ethylene, propane-1,3-diyl, propane-1,2-diyl, butane-1,4-diyl, 1-methylpropane-1,3-diyl, 2-methylpropane-1,3-diyl and 2-methylpropane-1,2-diyl groups.

Examples of the substituent of the aliphatic hydrocarbon group of A^(a42), A^(a43) and A^(a44) include a hydroxy group and a C₁ to C₆ alkoxy group.

s is preferably 0.

Examples of the group (a-g1) in which X^(a42) represents an oxygen atom include the following ones. In the formula, * and ** each represent a binding site, and ** represents a binding site to —O—CO—R^(a42).

Examples of the group (a-g1) in which X^(a42) represents a carbonyl group include the following ones.

Examples of the group (a-g1) in which X^(a42) represents a carbonyloxy group include the following ones.

Examples of the group (a-g1) in which X^(a42) represents an oxycarbonyl group include the following ones.

The structural unit represented by the formula (a4-1) is preferably structural units represented by the formula (a4-2) and the formula (a4-3):

wherein R^(f1) represents a hydrogen atom or a methyl group,

A^(f1) represent a C₁ to C₆ alkanediyl group, and

R^(f2) represents a C₁ to C₁₀ hydrocarbon group that has a fluorine atom.

Examples of the alkanediyl group of A^(f1) include a chain alkanediyl group such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl and hexane-1,6-diyl groups;

a branched alkanediyl group such as 1-methylpropane-1,3-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, 1-methylbutane-1,4-diyl and 2-methylbutane-1,4-diyl groups.

The hydrocarbon group of R^(f2) includes an aliphatic hydrocarbon group and an aromatic hydrocarbon group. The aliphatic hydrocarbon group includes a chain and a cyclic groups, and a combination thereof. The aliphatic hydrocarbon group is preferably an alkyl group and an alicyclic hydrocarbon group.

Examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl and 2-ethylhexyl groups.

Examples of the alicyclic hydrocarbon group include any of a monocyclic group and a polycyclic group. Examples of the monocyclic alicyclic hydrocarbon group include a cycloalkyl group such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclodecyl groups. Examples of the polycyclic hydrocarbon groups include decahydronaphthyl, adamantyl, 2-alkyladamantane-2-yl, 1-(adamantane-1-yl) norbornyl, methylnorbornyl and isobornyl groups.

Examples of the hydrocarbon group having a fluorine atom of R^(f2) include an alkyl group having a fluorine atom and an alicyclic hydrocarbon group having a fluorine atom.

Specific examples of an alkyl group having a fluorine atom include a fluorinated alkyl group such as difluoromethyl, trifluoromethyl, 1,1-difluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, perfluoroethyl, 1,1,2,2-tetrafluoropropyl, 1,1,2,2,3,3-hexafluoropropyl, perfluoroethylmethyl, 1-(trifluoromethyl)-1,2,2,2-tetrafluomethyl, perfluoropropyl, 1,1,2,2-tetrafluorobutyl, 1,1,2,2,3,3-hexafluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, perfluorobutyl, 1,1-bis(trifluoromethyl)methyl-2,2,2-trifluoroethyl, 2-(perfluoropropyl)ethyl, 1,1,2,2,3,3,4,4-octafluoropentyl, perfluoropentyl, 1, 1,2,2,3,3,4,4,5,5-decafluoropentyl, 1,1-bis(trifluoromethyl)2,2,3,3,3-pentafluoropropyl, perfluoropentyl, 2-(perfluorobutyl)ethyl, 1,1,2,2,3,3,4,4,5,5-decafluorohexyl, 1,1,2,2,3,3,4,4,5,5,6,6-dodeca fluorohexyl, perfluoropentylmethyl and perfluorohexyl groups.

Examples of the alicyclic hydrocarbon group having a fluorine atom include a fluorinated cycloalkyl group such as perfluorocyclohexyl and perfluoroadamantyl groups.

In the formula (a4-2), A^(f1) is preferably a C₂ to C₄ alkanediyl group, and more preferably ethylene group.

R^(f2) is preferably a C₁ to C₆ fluorinated alkyl group:

wherein R^(f11) represents a hydrogen atom or a methyl group,

A^(f11) represent a C₁ to C₆ alkanediyl group,

A^(f13) represents a C₁ to C₁₈ aliphatic hydrocarbon group that may has a fluorine atom,

X^(f12) represents an oxycarbonyl group or a carbonyloxy group,

A^(f14) represents a C₁ to C₁₇ aliphatic hydrocarbon group that may has a fluorine atom, and provided that at least one of A^(f13) and A^(f14) represents an aliphatic hydrocarbon group having a fluorine atom.

Examples of the alkanediyl group of A^(f11) are the same examples as the alkanediyl group of A^(f1).

Examples of the aliphatic hydrocarbon group of A^(f13) include any of a divalent chain or cyclic hydrocarbon group, or a combination thereof. The aliphatic hydrocarbon group may have a carbon-carbon unsaturated bond, and is preferably a saturated aliphatic hydrocarbon group.

The aliphatic hydrocarbon group that may has a fluorine atom of A^(f13) is the saturated aliphatic hydrocarbon group that may has a fluorine atom, and preferably a perfluoroalkandiyl group.

Examples of the divalent chain aliphatic hydrocarbon that may have a fluorine atom include an alkanediyl group such as methylene, ethylene, propanediyl, butanediyl and pentanediyl groups; a perfluoroalkanediyl group such as difluoromethylene, perfluoroethylene, perfluoropropanediyl, perfluorobutanediyl and perfluoropentanediyl groups.

The divalent cyclic aliphatic hydrocarbon group that may have a fluorine atom is any of monocyclic or polycyclic group.

Examples monocyclic aliphatic hydrocarbon group include cyclohexanediyl and perfluorocyclohexanediyl groups.

Examples polycyclic aliphatic hydrocarbon group include adamantanediyl, norbornanediyl, and perfluoroadamantanediyl groups.

Examples of the aliphatic hydrocarbon group of A^(f14) include any of a chain or a cyclic hydrocarbon group, or a combination thereof. The aliphatic hydrocarbon group may have a carbon-carbon unsaturated bond, and is preferably a saturated aliphatic hydrocarbon group.

The aliphatic hydrocarbon group that may has a fluorine atom of A^(f14) is preferably the saturated aliphatic hydrocarbon group that may have a fluorine atom.

Examples of the chain aliphatic hydrocarbon group that may have a halogen atom include trifluoromethyl, difluoromethyl, methyl, perfluoromethyl, 1,1,1-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, ethyl, perfluoropropyl, 1,1,1,2,2-pentafluoropropyl, propyl, perfluorobutyl, 1,1,2,2,3,3,4,4-octafluorobutyl, butyl, perfluoropentyl, 1,1,1,2,2,3,3,4,4-nonafluoropentyl, pentyl, hexyl, perfluorohexyl, hepthyl, perfluoroheptyl, octyl and perfluorooctyl groups.

The cyclic aliphatic hydrocarbon group that may have a halogen atom is any of monocyclic or polycyclic group. Examples of the group containing the monocyclic aliphatic hydrocarbon group include cyclopropylmethyl, cyclopropyl, cyclobutylmethyl, cyclopentyl, cyclohexyl and perfluorocyclohexyl groups. Examples of the group containing the polycyclic aliphatic hydrocarbon group include adamantyl, adamantylmethyl, norbornyl, norbornylmethyl, perfluoroadamantyl and perfluoroadamantylmethyl groups

In the formula (a4-3), A^(f11) is preferably ethylene group.

The aliphatic hydrocarbon group of A^(f13) is preferably a C₁ to C₆ aliphatic hydrocarbon group, more preferably a C₂ to C₃ aliphatic hydrocarbon group.

The aliphatic hydrocarbon group of A^(f14) is preferably a C₃ to C₁₂ aliphatic hydrocarbon group, more preferably a C₃ to C₁₀ aliphatic hydrocarbon group. Among these, A^(f14) is preferably a group containing a C₃ to C₁₂ alicyclic hydrocarbon group, more preferably cyclopropylmethyl, cyclopentyl, cyclohexyl, norbornyl and adamantyl group.

Examples of the structural unit (a4-2) include structural units represented by the formula (a4-1-1) to the formula (a4-1-22).

Examples of the structural unit (a4-3) include structural units presented by the formula (a4-1′-1) to the formula (A4-1′-22).

Examples of the structural unit (a4) include a structural unit presented by the formula (a4-4):

wherein R^(f21) represents a hydrogen atom or a methyl group,

A^(f21) represents —(CH₂)_(j1)—, —(CH₂)^(j2)—O—(CH₂)_(j3)— or —(CH₂)_(j4)—CO—O—(CH₂)_(j5)—,

j1 to j5 independently represents an integer of 1 to 6, and

R^(f22) represents a C₁ to C₁₀ hydrocarbon group having a fluorine atom.

Examples of the hydrocarbon group having a fluorine atom of R^(f22) are the same examples as the hydrocarbon group described in R^(f2) the formula (a4-2). R^(f22) is preferably a C₁ to C₁₀ alkyl having a fluorine atom or a C₃ to C₁₀ alicyclic hydrocarbon group having a fluorine atom, more preferably a C₁ to C₁₀ alkyl having a fluorine atom, and still more preferably a C₁ to C₆ alkyl having a fluorine atom.

In the formula (a4-4), A^(f21) is preferably —(CH₂)_(j)—, more preferably methylene or ethylene group, and still more preferably methylene group.

Examples of the structural unit represented by the formula (a4-4) include the following ones.

When the resin (A) contains the structural unit (a4), the proportion thereof is generally 1 to 20% by mole, preferably 2 to 15% by mole, more preferably 3 to 10% by mole, with respect to the total structural units (100% by mole) of the resin (A).

<Structural Unit (a5)>

Examples of the non-leaving hydrocarbon group in the structural unit (a5) include a chain, a branched or a cyclic hydrocarbon group. Among these, the structural unit (a5) is preferably a structural unit containing an alicyclic hydrocarbon group.

The structural unit (a5) is, for example, a structural unit represented by the formula (a5-1):

wherein R⁵¹ represents a hydrogen atom or a methyl group,

R⁵² represents a C₃ to C₁₈ alicyclic hydrocarbon group where a hydrogen atom may be replaced by a C₁ to C₈ aliphatic hydrocarbon group or a hydroxy group, provided that a hydrogen atom contained in the carbon atom bonded to L⁵¹ is not replaced by the C₁ to C₈ aliphatic hydrocarbon group, and

L⁵¹ represents a single bond or a C₁ to C₁₈ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group.

Examples of the alicyclic hydrocarbon group of R⁵² include any one of a monocyclic group or a polycyclic group. Examples of the monocyclic alicyclic hydrocarbon group include cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl groups. Examples of the polycyclic hydrocarbon group include adamantyl and norbornyl groups.

Examples of the C₁ to C₈ aliphatic hydrocarbon group include an alkyl group such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl and n-octyl groups.

Examples of the alicyclic hydrocarbon group having a substituent include 3-hydroxyadamantyl and 3-methyladamantyl.

R⁵² is preferably an unsubstituted C₃ to C₁₈ alicyclic hydrocarbon group, and more preferably adamantyl, norbornyl and cyclohexyl groups.

Examples of the divalent saturated hydrocarbon group of L⁵¹ include a divalent aliphatic saturated hydrocarbon group and a divalent alicyclic saturated hydrocarbon group, and a divalent aliphatic saturated hydrocarbon group is preferred.

Examples of the divalent aliphatic saturated hydrocarbon group include an alkanediyl such as methylene, ethylene, propanediyl, butanediyl and pentanediyl groups.

Examples of the divalent alicyclic saturated hydrocarbon group include any of a monocyclic group and a polycyclic group. Examples of the monocyclic alicyclic saturated hydrocarbon groups include cycloalkanediyl such as cyclopentanediyl and cyclohexanediyl groups. Examples of the polycyclic saturated hydrocarbon groups include adamantanediyl and norbornanediyl groups.

Examples of the group in which a methylene group contained in the saturated hydrocarbon group is replaced by an oxygen atom or a carbonyl group include groups represented by the formula (L1-1) to the formula (L1-4). In the formula (L1-1) to the formula (L1-4), * represents a binding site to an oxygen atom.

wherein X^(X1) represents an oxycarbonyl group or a carbonyloxy group,

L^(X1) represents a C₁ to C₁₆ divalent saturated aliphatic hydrocarbon group,

L^(X2) represents a single bond or a C₁ to C₁₅ divalent saturated hydrocarbon group, provided that the total carbon number contained in the group of L^(X1) and L^(X2) is 16 or less;

L^(X3) represents a single bond or a C₁ to C₁₇ divalent saturated aliphatic hydrocarbon group,

L^(X4) represents a single bond or a C₁ to C₁₆ divalent saturated hydrocarbon group, provided that the total carbon number contained in the group of L^(X3) and L^(X4) is 17 or less;

L^(X5) represents a C₁ to C₁₅ divalent saturated aliphatic hydrocarbon group,

L^(X6) and L^(X7) independently represents a single bond or a C₁ to C₁₄ divalent saturated hydrocarbon group, provided that the total carbon number contained in the group of L^(X5), L^(X6) and L^(X7) is 15 or less;

L^(X8) and L^(X9) independently represents a single bond or a C₁ to C₁₂ divalent saturated hydrocarbon group,

W^(X1) represents a C₃ to C₁₅ divalent saturated alicyclic hydrocarbon group, provided that the total carbon number contained in the group of L^(X8), L^(X9) and W^(X1) is 15 or less.

L^(X1) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L^(X2) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably a single bond.

L^(X3) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L^(X4) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L^(X5) is preferably a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L^(X6) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably methylene or ethylene group.

L^(X7) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group.

L^(X8) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably a single bond or methylene group.

L^(X9) is preferably a single bond or a C₁ to C₈ divalent saturated aliphatic hydrocarbon group, and more preferably a single bond or methylene group.

W^(X1) is preferably a C₃ to C₁₀ divalent saturated alicyclic hydrocarbon group, and more preferably cyclohexanediyl or adamantanediyl group.

Examples of the group represented by the formula (L1-1) include the following ones.

Examples of the group represented by the formula (L1-2) include the following ones.

Examples of the group represented by the formula (L1-3) include the following ones.

Examples of the group represented by the formula (L1-4) include the following ones.

L⁵¹ is preferably a single bond, methylene group, ethylene group or the groups represented by the formula (L1-1), and more preferably a single bond or the groups represented by the formula (L1-1).

Examples of the structural unit (a5-1) include the following ones.

When the resin (A) contains the structural unit (a5), the proportion thereof is generally 1 to 30% by mole, preferably 2 to 20% by mole, more preferably 3 to 15% by mole, with respect to the total structural units (100% by mole) of the resin (A).

The resin (A) may further include a structural unit a known structural units other than the structural unit described above.

The resin (A) preferably is a resin having the structural unit (a1) and the structural unit (s), that is, a copolymer of the monomer (a1) and the monomer (s). In this copolymer, the structural unit (a1) is preferably at least one of the structural unit (a1-1) and the structural unit (a1-2) (preferably the structural unit having a cyclohexyl group or a cyclopentyl group), and more preferably is at least two of the structural unit (a1-1), or the structural unit (a1-1) and the structural unit (a1-2) (preferably the structural unit having a cyclohexyl group or a cyclopentyl group).

The structural unit (s) is preferably at least one of the structural unit (a2) or the structural unit (a3). The structural unit (a2) is preferably the structural unit represented by the formula (a2-1). The structural unit (a3) is preferably at least one of the structural units (a3-1-1) to (a3-1-4), the structural units (a3-2-1) to (a3-2-4) and the structural units (a3-4-1) to (a3-4-2).

The proportion of the structural unit derived from the monomer having an adamantyl group (in particular, the structural unit (a1-1)) in the resin (A) is preferably 15% by mole or more with respect to the structural units (a1). As the mole ratio of the structural unit derived from the monomer having an adamantyl group increases within this range, the dry etching resistance of the resulting resist improves.

The resin (A) can be produced by a known polymerization method, for example, radical polymerization method, using one or more species of monomers as described above. The proportion of the structural unit in the resin (A) can be adjusted by changing the amount of a monomer used in polymerization.

The weight average molecular weight of the resin (A) is preferably 2,000 or more (more preferably 2,500 or more, and still more preferably 3,000 or more), and 50,000 or less (more preferably 30,000 or less, and still more preferably 15,000 or less).

The weight average molecular weight is a value determined by gel permeation chromatography using polystyrene as the standard product. The detailed condition of this analysis is described in Examples.

<Resin Other than Resin (A)>

A resist composition of the present invention may further include a resin other than the resin (A). Examples of the resin include a resin having only the structural unit (s).

The resin other than the resin (A) is preferably a resin including the structural unit (a4) (which is sometimes referred to as “resin (X)”). In the resin (X), the proportion of the structural unit (a4) is preferably 40% by mole or more, and more preferably 45% by mole or more, and still more preferably 50% by mole or more with respect to the total structural units (100% by mole) constituting the resin (X).

Examples of the structural unit in which the resin (X) may further include the structural unit (a2), the structural unit (a3) and other structural unit derived from a known monomer.

The weight average molecular weight of the resin (X) is preferably 8,000 or more (more preferably 10,000 or more), and 80,000 or less (more preferably 60,000 or less). The method of measuring of the weight average molecular weight of the resin (X) is the same as the resin (A).

When a resist composition contain the resin (X), the proportion thereof is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, and still more preferably 1 to 40 parts by mass, in particular preferably 2 to 30 parts by mass, with respect to the resin (A) (100 parts by mass).

The total proportion of the resin (A) and the resin other than the resin (A) is preferably 80% by mass to 99% by mass, more preferably 90% by mass to 99% by mass, with respect to the total amount of solid components of the resist composition.

The proportion of the solid components in the resist composition and that of the resins in the solid components can be measured with a known analytical method such as liquid chromatography and gas chromatography.

<Acid Generator (B)>

The acid generator (B) may be an ionic acid generator or a non-ionic acid generator. The ionic acid generator is preferred. Examples of the ionic acid generator include an ionic acid generator in combination of a known cation and a known anion.

Examples of the acid generator (B) include an organic sulfonic acid organic sulfonium salt and an acid generator described in JP2013-68914A, JP2013-3155A and JP2013-11905A, specifically salts represented by the formula (B1-1) to the formula (B1-30).

Among these, a salt which contains aryl sulfonium cation is preferred, salts represented by the formulae (B1-1), (B1-2), (B1-3), (B1-6), (B1-7), (B1-11), (B1-12), (B1-13), (B1-14), (B1-20), (B1-21), (B1-22), (B1-23), (B1-24), (B1-25), (B1-26) or (B1-29) are more preferred.

In the resist composition, the proportion of the salt (a) is preferably 0.1% by mass to 35% by mass, and more preferably 0.5% by mass to 30% by mass, and still more preferably 1% by mass to 25% by mass, with respect to total amount of solid components of the resist composition.

When the resist composition include the acid generator (B) in addition to the salt (a), the total proportion of the acid generator (B) and the salt (a) is preferably 1.5% by mass or more (and more preferably 3% by mass or more), and 40% by mass or less (and more preferably 35% by mass or less) with respect to 100% by mass of the resin (A).

The proportion of the acid generator (B) is preferably not less than 1 parts by mass (and more preferably not less than 3 parts by mass), and not more than 30 parts by mass (and more preferably not more than 25 parts by mass), with respect to 100 parts by mass of the resin (A). The resist composition of the present invention may contain a single acid generator (B) or as a combination of two or more acid generators (B), besides the salt (a).

The proportion of the salt (a) and the acid generator (B) (the mass ratio of salt (a)/acid generator (B)) may generally be 1/99 to 100/0, preferably 1/99 to 99/1, and more preferably 2/98 to 98/2, still more preferably 5/95 to 95/5.

<Solvent (E)>

The proportion of a solvent (E) is 90% by mass or more, preferably 92% by mass or more, and more preferably 94% by mass or more, and also preferably 99% by mass or less and more preferably 99.9% by mass or less. The proportion of the solvent (E) can be measured with a known analytical method such as, for example, liquid chromatography and gas chromatography.

Examples of the solvent (E) include glycol ether esters such as ethylcellosolve acetate, methylcellosolve acetate and propylene glycol monomethyl ether acetate; glycol ethers such as propylene glycol monomethyl ether; esters such as ethyl lactate, butyl acetate, amyl acetate and ethyl pyruvate; ketones such as acetone, methyl isobutyl ketone, 2-heptanone and cyclohexanone; and cyclic esters such as γ-butyrolactone. These solvents may be used as a single solvent or as a mixture of two or more solvents.

<Quencher>

The resist composition of the present invention may contain a quencher such as a basic nitrogen-containing organic compound and a salt which generates an acid weaker in acidity than an acid generated from the acid generators.

The proportion of the quencher is preferably 0.01% by mass to 5% by mass with respect to the total amount of solid components of the resist composition.

Examples of the basic nitrogen-containing organic compound include an amine and ammonium salts. The amine may be an aliphatic amine or an aromatic amine. The aliphatic amine includes any of a primary amine, secondary amine and tertiary amine.

Specific examples of the amine include 1-napthylamine, 2-napthylamine, aniline, diisopropylaniline, 2-, 3- or 4-methylaniline, 4-nitroaniline, N-methylaniline, N,N-dimethylaniline, diphenylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, triethylamine, trimethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, methyldibutylamine, methyldipentylamine, methyldihexylamine, methyldicyclohexylamine, methyldiheptylamine, methyldioctylamine, methyldinonylamine, methyldidecylamine, ethyldibutylamine, ethyldipentylamine, ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine, ethyldinonylamine, ethyldidecylamine, dicyclohexylmethylamine, tris[2-(2-methoxyethoxy)ethyl]amine, triisopropanolamine, ethylene diamine, tetramethylene diamine, hexamethylene diamine, 4,4′-diamino-1,2-diphenylethane, 4,4′-diamino-3,3′-dimethyldiphenylmethane, 4,4′-diamino-3,3′-diethyldiphenylmethane, 2,2′-methylenebisaniline, imidazole, 4-methylimidazole, pyridine, 4-methylpyridine, 1,2-di(2-pyridyl)ethane, 1,2-di(4-pyridyl)ethane, 1,2-di(2-pyridyl)ethene, 1,2-di(4-pyridyl)ethene, 1,3-di(4-pyridyl)propane, 1,2-di(4-pyridyloxy)ethane, di(2-pyridyl)ketone, 4,4′-dipyridyl sulfide, 4,4′-dipyridyl disulfide, 2,2′-dipyridylamine, 2,2′-dipicolylamine and bipyridine. Among these, diisopropylaniline is preferred, particularly 2,6-diisopropylaniline is more preferred.

Specific examples of the ammonium salt include tetramethylammonium hydroxide, tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide, tetrahexylammonium hydroxide, tetraoctylammonium hydroxide, phenyltrimethyl ammonium hydroxide, 3-(trifluoromethyl)phenyltrimethylammonium hydroxide, tetra-n-butyl ammonium salicylate and choline.

<Weak Acid Salt (D)>

The weak acid salt is a salt generating an acid which is lower in acidity than an acid generated from the acid generator (B) and salt (a). The “acidity” can be represented by acid dissociation constant, pKa, of an acid generated from a weak acid salt. Examples of the weak acid salt include a salt generating an acid of pKa represents generally more than −3, preferably −1 to 7, and more preferably 0 to 5.

Specific examples of the weak acid salt include the following salts, the weak acid inner salt of formula (D), and salts as disclosed in JP2012-229206A1, JP2012-6908A1, JP2012-72109A1, JP2011-39502A1 and JP2011-191745A1, preferably the salt of formula (D).

wherein R^(D1) and R^(D2) in each occurrence independently represent a C₁ to C₁₂ hydrocarbon group, a C₁ to C₆ alkoxy group, a C₂ to C₇ acyl group, a C₂ to C₇ acyloxy group, a C₂ to C₇ alkoxycarbonyl group, a nitro group or a halogen atom, and

m′ and n′ independently represent an integer of 0 to 4.

The hydrocarbon group of R^(D1) and R^(D2) includes any of an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a combination thereof.

Examples of the aliphatic hydrocarbon group include an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, hexyl and nonyl groups.

The alicyclic hydrocarbon group is any one of monocyclic or polycyclic hydrocarbon group, and saturated or unsaturated hydrocarbon group. Examples thereof include a cycloalkyl group such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclononyl and cyclododecyl groups; adamantyl and norbornyl groups. The alicyclic hydrocarbon group is preferably saturated hydrocarbon group.

Examples of the aromatic hydrocarbon group include an aryl group such as phenyl, 1-naphthyl, 2-naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-propylphenyl, 4-isopropylphenyl, 4-butylphenyl, 4-tert-butylphenyl, 4-hexylphenyl, 4-cyclohexylphenyl, anthryl, p-adamantylphenyl, tolyl, xylyl, cumenyl, mesityl, biphenyl, phenanthryl, 2,6-diethylphenyl and 2-methyl-6-ethylphenyl groups.

Examples of the combination thereof include an alkyl-cycloalkyl, a cycloalkyl-alkyl, aralkyl (e.g., phenylmethyl, 1-phenylethyl, 2-phenylethyl, 1-phenyl-1-propyl, 1-phenyl-2-propyl, 2-phenyl-2-propyl, 3-phenyl-1-propyl, 4-phenyl-1-butyl, 5-phenyl-1-pentyl and 6-phenyl-1-hexyl groups) groups.

Examples of the alkoxy group include methoxy and ethoxy groups.

Examples of the acyl group include acetyl, propanonyl, benzoyl and cyclohexanecarbonyl groups.

Examples of the acyloxy group include a group in which oxy group (—O—) bonds to an acyl group.

Examples of the alkoxycarbonyl group include a group in which the carbonyl group (—CO—) bonds to the alkoxy group.

Examples of the halogen atom include a chlorine atom, a fluorine atom and bromine atom.

In the formula (D), R^(D1) and R^(D2) in each occurrence independently preferably represent a C₁ to C₈ alkyl group, a C₃ to C₁₀ cycloalkyl group, a C₁ to C₆ alkoxy group, a C₂ to C₄ acyl group, a C₂ to C₄ acyloxy group, a C₂ to C₄ alkoxycarbonyl group, a nitro group or a halogen atom.

m′ and n′ independently preferably represent an integer of 0 to 3, more preferably an integer of 0 to 2, and more preferably 0.

Specific examples of the weak acid inner salt include the following ones.

The weak acid inner salt of formula (D) can be produced by a method described in “Tetrahedron Vol. 45, No. 19, p6281-6296”. Also, commercially available compounds can be used as the compound (D).

In the resist composition of the present invention, the proportion of the salt which generates an acid weaker in acidity than an acid generated from the acid generator, for example, the weak acid inner salt (D) is preferably 0.01% by mass to 5% by mass, more preferably 0.01% by mass to 4% by mass, and still more preferably 0.01% by mass to 3% by mass with respect to total amount of solid components of the resist composition.

<Other Ingredient>

The resist composition can also include other ingredient (which is sometimes referred to as “other ingredient (F)”). The other ingredient (F) includes various additives such as sensitizers, dissolution inhibitors, surfactants, stabilizers, and dyes, as needed.

<Preparing the Resist Composition>

The present resist composition can be prepared by mixing the resin (A), the salt (a) of the present invention, the acid generator (B), the resin other than the resin (A), the quencher, the weak acid inner salt (D), the solvent (E) and the other ingredient (F), as needed. There is no particular limitation on the order of mixing. The mixing may be performed in an arbitrary order. The temperature of mixing may be adjusted to an appropriate temperature within the range of 10 to 40° C., depending on the kinds of the resin and solubility in the solvent (E) of the resin. The time of mixing may be adjusted to an appropriate time within the range of 0.5 to 24 hours, depending on the mixing temperature. There is no particular limitation to the tool for mixing. An agitation mixing may be adopted.

After mixing the above ingredients, the present resist compositions can be prepared by filtering the mixture through a filter having about 0.003 to 0.2 μm of its pore diameter.

<Method for Producing Resist Pattern>

The method for producing a resist pattern of the present invention includes the steps of:

(1) applying the resist composition of the present invention onto a substrate;

(2) drying the applied composition to form a composition layer;

(3) exposing the composition layer;

(4) heating the exposed composition layer, and

(5) developing the heated composition layer.

Applying the resist composition onto the substrate can generally be carried out through the use of a resist application device, such as a spin coater known in the field of semiconductor microfabrication technique. Examples of the substrate include inorganic substrates such as silicon wafer. The substrate may be washed, and an organic antireflection film may be formed on the substrate by use of a commercially available antireflection composition, before the application of the resist composition.

The solvent evaporates from the resist composition and a composition layer with the solvent removed is formed. Drying the applied composition layer, for example, can be carried out using a heating device such as a hotplate (so-called “prebake”), a decompression device, or a combination thereof. The temperature is preferably within the range of 50 to 200° C. The time for heating is preferably 10 to 180 seconds. The pressure is preferably within the range of 1 to 1.0×10⁵ Pa.

The composition layer thus obtained is generally exposed using an exposure apparatus or a liquid immersion exposure apparatus. The exposure is generally carried out using with various types of exposure light source, such as irradiation with ultraviolet lasers, i.e., KrF excimer laser (wavelength: 248 nm), ArF excimer laser (wavelength: 193 nm), F₂ excimer laser (wavelength: 157 nm), irradiation with harmonic laser light of far-ultraviolet or vacuum ultra violet wavelength-converted laser light from a solid-state laser source (YAG or semiconductor laser or the like), or irradiation with electron beam or EUV or the like. In the specification, such exposure to radiation is sometimes referred to be collectively called as exposure. The exposure is generally carried out through a mask that corresponds to the desired pattern. When electron beam is used as the exposure light source, direct writing without using a mask can be carried out.

After exposure, the composition layer is subjected to a heat treatment (so-called “post-exposure bake”) to promote the deprotection reaction. The heat treatment can be carried out using a heating device such as a hotplate. The heating temperature is generally in the range of 50 to 200 degree C., preferably in the range of 70 to 150 degree C.

The developing of the baked composition film is usually carried out with a developer using a development apparatus. Developing can be conducted in the manner of dipping method, paddle method, spray method and dynamic dispensing method. Temperature for developing is generally 5 to 60 degree C. The time for developing is preferably 5 to 300 seconds.

The photoresist pattern obtained from the photoresist composition may be a positive one or a negative one by selecting suitable developer.

The development for obtaining a positive photoresist pattern is usually carried out with an alkaline developer. The alkaline developer to be used may be any one of various alkaline aqueous solution used in the art. Generally, an aqueous solution of tetramethylammonium hydroxide or (2-hydroxyethyl)trimethylammonium hydroxide (commonly known as “choline”) is often used. The surfactant may be contained in the alkaline developer.

After development, the resist pattern formed is preferably washed with ultrapure water, and the residual water remained on the resist film or on the substrate is preferably removed therefrom.

The development for obtaining a negative photoresist pattern is usually carried out with a developer containing an organic solvent. The organic solvent to be used may be any one of various organic solvents used in the art, examples of which include ketone solvents such as 2-hexanone, 2-heptanone; glycol ether ester solvents such as propylene glycol monomethyl ether acetate; ester solvents such as the butyl acetate; glycol ether solvents such as the propylene glycol monomethyl ether; amide solvents such as N,N-dimethylacetamide; aromatic hydrocarbon solvents such as anisole.

In the developer containing an organic solvent, the amount of organic solvents is preferably 90% by mass to 100% by mass, more preferably 95% by mass to 100% by mass of the developer. The developer still more preferably consists essentially of organic solvents.

Among these, the developer containing an organic solvent preferably contains butyl acetate and/or 2-heptanone. In the developer containing an organic solvent, the total amount of butyl acetate and 2-heptanone is preferably 50% by mass to 100% by mass of the developer, more preferably 90% by mass to 100% by mass of the developer. The developer still more preferably consists essentially of butyl acetate and/or 2-heptanone.

Developers containing an organic solvent may contain a surfactant. Also, the developer containing an organic solvent may include a little water.

The developing with a developer containing an organic solvent can be finished by replacing the developer by another solvent.

After development, the photoresist pattern formed is preferably washed with a rinse agent. Such rinse agent is not unlimited provided that it does not detract a photoresist pattern. Examples of the agent include solvents which contain organic solvents other than the above-mentioned developers, such as alcohol agents or ester agents.

After washing, the residual rinse agent remained on the substrate or photoresist film is preferably removed therefrom.

<Application>

The resist composition of the present invention is useful for excimer laser lithography such as with ArF, KrF, electron beam (EB) exposure lithography or extreme-ultraviolet (EUV) exposure lithography, and is more useful for electron beam (EB) exposure lithography, ArF excimer laser exposure lithography and extreme-ultraviolet (EUV) exposure lithography.

The resist composition of the present invention can be used in semiconductor microfabrication.

EXAMPLES

All percentages and parts expressing the contents or amounts used in the Examples and Comparative Examples are based on mass, unless otherwise specified.

The weight average molecular weight is a value determined by gel permeation chromatography.

Column: TSK gel Multipore HXL-M×3+guardcolumn (Tosoh Co. Ltd.)

Eluant: tetrahydrofuran

Flow rate: 1.0 mL/min

Detecting device: RI detector

Column temperature: 40° C.

Injection amount: 100 μL

Standard material for calculating molecular weight: standard polyethylene (Tosoh Co. ltd.)

Structures of compounds were determined by mass spectrometry (Liquid Chromatography: 1100 Type, manufactured by AGILENT TECHNOLOGIES LTD., Mass Spectrometry: LC/MSD Type, manufactured by AGILENT TECHNOLOGIES LTD.). The value of the peak in the mass spectrometry is referred to as “MASS”.

Example 1: Synthesis of the Salt Represented by the Formula (I-1)

A salt represented by the formula (I-1-a) was synthesized by the method described in JP2007-224008A.

In to a reactor, 7.00 parts of the salt represented by the formula (I-1-a), 6.50 parts of the compound represented by the formula (I-1-b), 35 parts of chloroform, 14 parts of acetonitrile, 14 parts of dimethylformamide were charged and stirred at 23 degree C. for about 30 minutes. Then, 0.07 parts of p-toluenesulfonic acid was added thereto, and the obtained solution was heated to reflux and stirred for 3 hours. The resulting reactant was cooled into 23 degree C., 155 parts of chloroform was added thereto and the obtained mixture was stirred, followed by filtrating. To the obtained filtrate, 40 parts of 5% of sodium hydrogen carbonate solution was added and the obtained mixture was stirred at 23 degree C. for 30 minutes. Then, the mixture was left still to separate an organic layer. 45 parts of ion exchanged water was added to the obtained organic layer and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step was conducted three times. 95 part of ethyl acetate was added to the obtained organic layer and the obtained mixture was stirred, followed by removing a supernatant therefrom. The obtained residue was dissolved in acetonitrile. Then the mixture was concentrated, whereby giving 4.38 parts of the salt represented by the formula (I-1-c).

In to a reactor, 2.20 parts of the compound represented by the formula (I-1-d) and 8.82 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. Then, 1.88 parts of the salt represented by the formula (I-1-e) was added thereto for 15 minutes and the obtained mixture was stirred at 50 degree C. for 1 hour. To the resultant, 2.00 parts of the salt represented by the formula (I-1-c) was added and the obtained mixture was stirred at 50 degree C. for 10 hours. The reactant was cooled into 23 degree C., 110 parts of chloroform and 35 parts of ion exchanged water were added thereto, the obtained mixture was stirred and left still to separate an organic layer. To the obtained organic layer, 35 parts of ion exchanged water was added, followed by separating an organic layer to wash with water. The washing step was conducted seven times. The obtained organic layer was concentrated, to the obtained residue, 3 parts of acetonitrile, 16 part of ethyl acetate and 16 parts of t-butylmethylether were added, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 1.45 parts of the salt represented by the formula (I-1).

MS(ESI(+)Spectrum): M⁺ 263.1

MS(ESI(−)Spectrum): M⁻ 793.3

Example 2: Synthesis of the Salt Represented by the Formula (I-2)

In to a reactor, 4.12 parts of the compound represented by the formula (I-2-d) and 42 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. Then, 3.51 parts of the compound represented by the formula (I-1-e) was added to the resulting solution for 15 minutes, and the obtained mixture was stirred at 60 degree C. for an hour. To the resulting reactant, 3.74 parts of the salt represented by the formula (I-1-c) was added and the obtained mixture was stirred at 60 degree C. for about 48 hours. The resulting reactant was cooled into 23 degree C., 100 parts of chloroform and 30 parts of ion exchanged water were added thereto and the obtained mixture was stirred. Then, the mixture was left still to separate an organic layer. To the separated organic layer, 30 parts of ion exchanged water was added, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step was conducted seven times. The obtained organic layer was concentrated, to the obtained residue, 6 parts of acetonitrile, 25 part of ethyl acetate and 25 parts of t-butyl methyl ether were added, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 2.48 parts of the salt represented by the formula (I-2).

MS(ESI(+)Spectrum): M⁺ 263.1

MS(ESI(−)Spectrum): M⁻ 797.3

Example 3: Synthesis of the Salt Represented by the Formula (I-3)

In to a reactor, 3.82 parts of the compound represented by the formula (I-3-d) and 38 parts of acetonitrile were charged, and the obtained mixture was stirred at 23 degree C. for about 30 minutes. Then, 3.51 parts of the compound represented by the formula (I-1-e) was added to the resulting solution for 15 minutes, and the obtained mixture was stirred at 60 degree C. for an hour. To the resulting reactant, 3.74 parts of the salt represented by the formula (I-1-c) was added and the obtained mixture was stirred at 60 degree C. for about 48 hours. The resulting reactant was cooled into 23 degree C., 100 parts of chloroform and 30 parts of ion exchanged water were added thereto and the obtained mixture was stirred. Then, the mixture was left still to separate an organic layer. To the organic layer, 30 parts of ion exchanged water was added and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted seven times. The obtained organic layer was concentrated, then 6 parts of acetonitrile and 25 parts of t-butylmethylether were added to the obtained residue, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 4.57 parts of the salt represented by the formula (I-3).

MS(ESI(+)Spectrum): M⁺ 263.1

MS(ESI(−)Spectrum): M⁻ 765.3

Example 4: Synthesis of the Salt Represented by the Formula (I-4)

A salt represented by the formula (I-4-a) was synthesized by the method described in JP2012-224611A.

In to a reactor, 10.00 parts of the salt represented by the formula (I-4-a), 9.71 parts of the compound represented by the formula (I-1-b), 100 parts of dimethylformamide were charged and stirred at 23 degree C. for about 30 minutes. Then, 0.10 parts of p-toluenesulfonic acid was added to the resulting solution, and the obtained solution was heated to reflux and stirred for 3 hours. The resulting reactant was cooled into 23 degree C., 240 parts of chloroform was added thereto and the obtained mixture was stirred, followed by filtrating. To the obtained filtrate, 40 parts of 5% of aqueous sodium hydrogen carbonate solution was added and the obtained mixture was stirred at 23 degree C. for 30 minutes. Then, the mixture was left still to separate an organic layer. To the obtained organic layer, 70 parts of ion exchanged water was added, and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step was conducted three times. The obtained organic layer was concentrated, whereby giving 6.33 parts of the salt represented by the formula (I-4-c).

In to a reactor, 2.20 parts of the compound represented by the formula (I-1-d) and 8.82 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. Then, 1.88 parts of the compound represented by the formula (I-1-e) was added to the resulting solution for 15 minutes and the obtained mixture was stirred at 50 degree C. for 1 hour. To the resultant, 1.93 parts of the salt represented by the formula (I-4-c) was added, and the obtained mixture was stirred at 50 degree C. for 10 hours. The reactant was cooled into 23 degree C., 100 parts of chloroform and 35 parts of ion exchanged water were added thereto, the obtained mixture was stirred and left still to separate an organic layer. To the obtained organic layer, 35 parts of ion exchanged water was added, and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted five times. The obtained organic layer was concentrated, 3 parts of acetonitrile, 20 part of ethyl acetate and 20 parts of t-butylmethylether were added to the obtained residue, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 1.38 parts of the salt represented by the formula (I-4).

MS(ESI(+)Spectrum): M⁺ 237.1

MS(ESI(−)Spectrum): M⁻ 793.3

Example 5: Synthesis of the Salt Represented by the Formula (I-5)

In to a reactor, 13.04 parts of the compound represented by the formula (I-5-a), 15.22 parts of the compound represented by the formula (I-5-b), 200 parts of chloroform were charged and stirred at 23 degree C. for about 30 minutes. To the mixture, 0.61 parts of sulfuric acid was added, and the obtained solution was heated to reflux at 60 degree C. for 12 hours in the presence of molecular sieve. The resulting reactant was cooled into 23 degree C., 65 parts of 10% aqueous potassium carbonate solution was added thereto and the obtained mixture was stirred at 23 degree C. for 30 minutes. Then, the mixture was left still to separate an organic layer. To the obtained organic layer, 80 parts of ion exchanged water was added, and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted four times. The washed organic layer was concentrated. To the obtained residue, 25 Parts of methanol and 25 parts of ion exchanged water were added and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by filtrating, whereby giving 12.93 parts of the compound represented by the formula (I-5-c).

In to a reactor, 12.93 parts of the compound represented by the formula (I-5-c) and 65 parts of acetone were added and stirred at 0 degree C. for 30 minutes. To the mixture, 44 parts of 5% aqueous sodium hydroxide solution was added, and the obtained solution was stirred at 23 degree C. for 18 hours. To the obtained reactant, 280 parts of 5% aqueous oxalic acid solution and 250 parts of ethyl acetate were added, and stirred at 23 degree C. for 30 minutes. Then, the mixture was left still to separate an organic layer. To the obtained organic layer, 150 parts of ion exchanged water was added, and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted three times. The washed organic layer was concentrated. To the obtained residue, 50 parts of n-heptane was added, and the mixture was stirred at 23 degree C. for 30 minutes, followed by filtrating, whereby giving 9.54 parts of the salt represented by the formula (I-2).

In to a reactor, 8.65 parts of the compound represented by the formula (I-5-d) and 34.60 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. Then, 4.23 parts of the compound represented by the formula (I-1-e) was added to the resulting solution for 15 minutes and the obtained mixture was stirred at 50 degree C. for 1 hour. To the resultant, 6.00 parts of the salt represented by the formula (I-1-c) was added for 15 minutes and the obtained mixture was stirred at 50 degree C. for 18 hours. The reactant was cooled into 23 degree C., 100 parts of chloroform and 35 parts of ion exchanged water were added thereto, the obtained mixture was stirred and left still to separate an organic layer. To the obtained organic layer, 35 parts of ion exchanged water was added and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted five times. The obtained organic layer was concentrated, 3 parts of acetonitrile, 20 part of ethyl acetate and 100 parts of t-butylmethylether were added to the obtained residue, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 2.09 parts of the salt represented by the formula (I-5).

MS(ESI(+)Spectrum): M⁺ 263.1

MS(ESI(−)Spectrum): M⁻ 1081.3

Example 6: Synthesis of the Salt Represented by the Formula (I-6)

In to a reactor, 50 parts of the salt represented by the formula (I-6-a), 10.33 parts of the compound represented by the formula (I-6-b), 350 parts of chloroform were charged and stirred at 23 degree C. for about 30 minutes. To the mixture, 0.20 parts of copper acetate (II) was added, and the obtained solution was heated to reflux at 80 degree C. for 2 hours to concentrate. To the resulting concentrate, 440 parts of tert-butylmethylether was added and the mixture was stirred, followed by filtrating, whereby giving 32.96 parts of the salt represented by the formula (I-6-c).

To 10 parts of tetrahydrofuran, 2.21 parts of lithium aluminium hydride was added at 5 degree C. and the mixture was stirred at 5 degree C. for about 30 minutes. Then, 8.22 parts of the salt represented by the formula (I-6-d) and 30 parts of tetrahydrofuran were added to the resulting solution for 1 hour and the obtained mixture was stirred at 23 degree C. for 18 hours. To the resultant, 30 parts of 1N hydrochloric acid was added and concentrated. To the obtained concentrate, 82 parts of acetonitrile was added and the mixture was stirred, followed by filtrating. The obtained filtrate was concentrated, whereby giving 6.28 parts of the salt represented by the formula (I-6-e).

13.25 parts of the compound represented by the formula (I-6-0 and 40 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. 11.63 parts of the compound represented by the formula (I-1-e) was added to the obtained solution and the obtained mixture was stirred at 40 degree C. for 1 hour. To the resultant, mixed solution of 6.28 parts of the salt represented by the formula (I-6-h) and 13.20 parts of acetonitrile was added and the obtained mixture was stirred at 23 degree C. for 16 hours. To the reactant, 30 parts of acetonitrile was added, followed by filtrating. Then the filtrate was concentrated, whereby giving 9.06 parts of the salt represented by the formula (I-6-i).

In to a reactor, 9.06 parts of the salt represented by the formula (I-64), 11.89 parts of the salt represented by the formula (I-6-c), 20 parts of acetonitrile, 63 parts of chloroform and 31.44 parts of 5% aqueous oxalic acid solution were charged, and stirred at 23 degree C. for about 30 minutes and left still to separate an organic phase. Then, 21 parts of 5% aqueous oxalic acid solution was added to the separated layer and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer. The washing step was conducted three times. To the obtained organic layer, 21 parts of 5% aqueous sodium hydrogen carbonate solution was added, and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step was conducted twice. To the obtained organic layer, 21 parts of ion exchanged water was added and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted three times. The obtained organic layer was concentrated. To the obtained residue, 80 parts of acetonitrile and 60 parts of ethyl acetate were added, followed by filtrating, whereby giving 4.53 parts of the salt represented by the formula (I-6-j).

In to a reactor, 10.25 parts of the salt represented by the formula (I-6-j), 9.71 parts of the compound represented by the formula (I-1-b), 100 parts of dimethylformamide were charged and stirred at 23 degree C. for about 30 minutes. Then, 0.10 parts of p-toluenesulfonic acid was added to the resulting solution, and the obtained solution was heated to reflux and stirred for 3 hours. The resulting reactant was cooled into 23 degree C., 250 parts of chloroform was added thereto and the obtained mixture was stirred, followed by filtrating. To the obtained filtrate, 40 parts of 5% of aqueous sodium hydrogen carbonate solution was added and the obtained mixture was stirred at 23 degree C. for 30 minutes. Then, the mixture was left still to separate an organic layer. To the obtained organic layer, 70 parts of ion exchanged water was added, and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step was conducted three times. The obtained organic layer was concentrated, whereby giving 6.38 parts of the salt represented by the formula (I-6-l).

In to a reactor, 2.20 parts of the compound represented by the formula (I-1-d) and 8.82 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. Then, 1.88 parts of the compound represented by the formula (I-1-e) was added to the resulting solution for 15 minutes and the obtained mixture was stirred at 50 degree C. for 1 hour. To the resultant, 1.93 parts of the salt represented by the formula (I-6-1) was added and the obtained mixture was stirred at 50 degree C. for 10 hours. The reactant was cooled into 23 degree C., 100 parts of chloroform and 35 parts of ion exchanged water were added thereto, the obtained mixture was stirred and left still to separate an organic layer. To the obtained organic layer, 35 parts of ion exchanged water was added, and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted five times. The obtained organic layer was concentrated, to the obtained residue, 3 parts of acetonitrile, 20 part of ethyl acetate and 50 parts of t-butyl methyl ether were added and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 1.25 parts of the salt represented by the formula (I-6).

MS(ESI(+)Spectrum): M⁺ 237.1

MS(ESI(−)Spectrum): M⁻ 807.3

Example 7: Synthesis of the Salt Represented by the Formula (I-7)

In to a reactor, 8.65 parts of the compound represented by the formula (I-5-d) and 34.60 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. Then, 4.23 parts of the compound represented by the formula (I-1-e) was added to the resulting solution for 15 minutes and the obtained mixture was stirred at 50 degree C. for 1 hour. To the resultant, 5.783 parts of the salt represented by the formula (I-4-c) was added for 15 minutes and the obtained mixture was stirred at 50 degree C. for 18 hours. The reactant was cooled into 23 degree C., 100 parts of chloroform and 35 parts of ion exchanged water were added thereto, the obtained mixture was stirred and left still to separate an organic layer. To the obtained organic layer, 35 parts of ion exchanged water was added and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted five times. The obtained organic layer was concentrated, 20 parts of acetonitrile and 20 parts of t-butyl methyl ether were added to the obtained residue, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 1.96 parts of the salt represented by the formula (I-7).

MS(ESI(+)Spectrum): M⁺ 237.1

MS(ESI(−)Spectrum): M⁻ 1081.3

Example 8: Synthesis of the Salt Represented by the Formula (I-8)

A salt represented by the formula (I-8-a) was synthesized by the method described in JP2012-224611A.

In to a reactor, 10.00 parts of the salt represented by the formula (I-8-a), 6.57 parts of the compound represented by the formula (I-8-b), 100 parts of chloroform were charged and stirred at 23 degree C. for about 30 minutes. Then, 0.10 parts of p-toluenesulfonic acid was added to the resulting solution, and the obtained solution was heated to reflux and stirred for 3 hours. The resulting reactant was cooled into 23 degree C., 240 parts of chloroform was added thereto and the obtained mixture was stirred, followed by filtrating. To the obtained filtrate, 45 parts of 5% of aqueous sodium hydrogen carbonate solution was added and the obtained mixture was stirred at 23 degree C. for 30 minutes. Then, the mixture was left still to separate an organic layer. To the obtained organic layer, 70 parts of ion exchanged water was added, and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted three times. The obtained organic layer was concentrated, whereby giving 11.01 parts of the salt represented by the formula (I-8-c).

In to a reactor, 2.20 parts of the compound represented by the formula (I-1-d) and 8.82 parts of acetonitrile were charged and stirred at 23 degree C. for about 30 minutes. Then, 1.88 parts of the compound represented by the formula (I-1-e) was added to the resulting solution for 15 minutes and the obtained mixture was stirred at 50 degree C. for 1 hour. To the resultant, 3.60 parts of the salt represented by the formula (I-8-c) was added and the obtained mixture was stirred at 50 degree C. for 10 hours. The reactant was cooled into 23 degree C., 100 parts of chloroform and 35 parts of ion exchanged water were added thereto, and the obtained mixture was stirred and left still to separate an organic layer. 35 parts of ion exchanged water was added to the obtained organic layer and stirred at 23 degree C. for about 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted five times. The obtained organic layer was concentrated, 10 parts of acetonitrile and 120 parts of t-butylmethylether were added to the obtained residue, and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by removing a supernatant therefrom. Then the residue was concentrated, whereby giving 2.68 parts of the salt represented by the formula (I-8).

MS(ESI(+)Spectrum): M⁺ 237.1

MS(ESI(−)Spectrum): M⁻ 573.2

Synthesis Example 1: Synthesis of the Salt Represented by the Formula (B1-5)

In to a reactor, 50.49 parts of compound represented by formula (B1-5-a) and 252.44 parts of chloroform were charged and stirred at 23 degree C. for 30 minutes. Then 16.27 parts of compound represented by formula (B1-5-b) were dropped thereinto and the obtained mixture was stirred at 23 degree C. for one hour to obtain a solution containing the compound represented by formula (B1-5-c). To the obtained solution, 48.80 parts of compound represented by formula (B1-5-d) and 84.15 parts of ion-exchanged water were added and the obtained mixture was stirred at 23 degree C. for 12 hours. From the obtained solution which had two phases, the chloroform phase was collected and then 84.15 parts of ion-exchanged water were added for washing. The washing step was conducted five times. To the washed chloroform phase, 3.88 parts of active carbon were added and the obtained mixture was stirred, followed by filtrating. The collected filtrate was concentrated and then 125.87 parts of acetonitrile were added thereto and the obtained mixture was stirred, followed by being concentrated. 20.62 parts of acetonitrile and 309.30 parts of tert-butylmethylether were added to the obtained residues, followed by being stirred at 23 degree C. for about 30 minutes. Then the supernatant was removed therefrom, and the residues were concentrated. To the concentrated residues, 200 parts of n-heptane were added and the obtained mixture was stirred at 23 degree C. for about 30 minutes, followed by being filtrated, whereby giving 61.54 parts of salt represented by formula (B1-5).

MASS(ESI(+)Spectrum): M⁺ 375.2

MASS(ESI(−)Spectrum): M⁻ 339.1

Synthesis Example 2: Synthesis of the Salt Represented by the Formula (B1-21)

The compound represented by formula (B1-21-b) was produced according to a method recited in JP2008-209917A1.

In to a reactor, 30.00 parts of compound represented by formula (B1-21-b) and 35.50 parts of salt represented by formula (B1-21-a), 100 parts of chloroform and 50 parts of ion exchanged water were charged and stirred at 23 degree C. for about 15 hours. The obtained reaction mixture, which had two layers, was separated into a chloroform layer therefrom. To the chloroform layer, 30 parts of ion exchanged water was added and washed with it. These steps were conducted five times. Then the washed layer was concentrated, and then, 100 parts of tert-butylmethylether was added to the obtained residues and the obtained mixture was stirred at 23 degree C. for about 30 minutes. The resulting mixture was filtrated, whereby giving 48.57 parts of salt represented by formula (B1-21-c).

In to a reactor, 20.00 parts of salt represented by formula (B1-21-c), 2.84 parts of compound represented by formula (B1-21-d) and 250 parts of monochlorobenzene were charged and stirred at 23 degree C. for 30 minutes. To the resulting mixture, 0.21 parts of dibenzoic acid copper (II) was added and the obtained mixture was stirred at 100 degree C. for 1 hour. The reaction mixture was concentrated, and then, 200 parts of chloroform and 50 parts of ion exchanged water were added to the obtained residues and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The following washing step was conducted five times. 50 parts of ion exchanged water were added to the obtained organic layer, and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer. The obtained organic layer was concentrated, and then the obtained residues were dissolved in 53.51 parts of acetonitrile. Then the mixture was concentrated, and then 113.05 parts of tert-butylmethylether was added thereto and the obtained mixture was stirred, followed by filtrating it, whereby giving 10.47 parts of salt represented by formula (B1-21).

MASS(ESI(+)Spectrum): M⁺ 237.1

MASS(ESI(−)Spectrum): M⁻ 339.1

Synthesis Example 3: Synthesis of the Salt Represented by the Formula (B1-22)

In to a reactor, 11.26 parts of salt represented by formula (B1-21-a), 10.00 parts of compound represented by formula (B1-22-b), 50 parts of chloroform and 25 parts of ion exchanged water were charged and stirred at 23 degree C. for about 15 hours. The obtained reaction mixture, which had two layers, was separated into a chloroform layer therefrom. To the chloroform layer, 15 parts of ion exchanged water were added and washed with it: These steps were conducted five times. Then the washed layer was concentrated, and then, 50 parts of tert-butyl methyl ether was added to the obtained residues and the obtained mixture was stirred at 23 degree C. for about 30 minutes. The resulting mixture was filtrated, whereby giving 11.75 parts of salt represented by formula (B1-22-c).

In to a reactor, 11.71 parts of salt represented by formula (B1-22-c), 1.7 parts of compound represented by formula (B1-22-d) and 46.84 parts of monochlorobenzene were charged and stirred at 23 degree C. for 30 minutes. To the resulting mixture, 0.12 parts of dibenzoic acid copper (II) was added and the obtained mixture was stirred at 100 degree C. for 30 minutes. The reaction mixture was concentrated, and then 50 parts of chloroform and 12.5 parts of ion exchanged water were added to the obtained residues, and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. 12.5 parts of ion exchanged water was added to the obtained organic layer and the obtained mixture was stirred at 23 degree C. for 30 minutes, followed by separating an organic layer to wash with water. The washing step with water was conducted eight times. Then the mixture was concentrated, and 50 parts of tert-butylmethylether were added thereto and the obtained mixture was stirred, followed by filtrating it, whereby giving 6.84 parts of salt represented by formula (B1-22).

MASS(ESI(+)Spectrum): M⁺ 237.1

MASS(ESI(−)Spectrum): M⁻ 323.0

Synthesis Examples of Resins

The monomers used for Synthesis Examples of the resins are shown below. These monomers are referred to as “monomer (X)” where “(X)” is the symbol of the formula representing the structure of each monomer.

Synthesis Example 4: Synthesis of Resin A1

Monomer (a1-1-3), monomer (a1-2-9), monomer (a2-1-3) and monomer (a3-4-2) were mixed together with the mole ratio of monomer (a1-1-3), monomer (a1-2-9), monomer (a2-1-3) and monomer (a3-4-2)=45:14:2.5:38.5, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.5 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1% by mole and 3% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 73° C. Then, the obtained reacted mixture was poured into a large amount of a mixture of methanol and water to precipitate a resin. The obtained resin was filtrated. Thus obtained resin was dissolved in another propyleneglycolmonomethylether acetate to obtain a solution, and the solution was poured into a large amount of a mixture of methanol and water to precipitate the resin. The obtained resin was filtrated. These operations were repeated twice, to obtain a copolymer having a weight average molecular weight of about 7600, in 68% yield. This resin, which had the structural units of the following formulae, was referred to as Resin A1.

Synthesis Example 5: Synthesis of Resin A2

Monomer (a1-1-2), monomer (a2-1-1) and monomer (a3-1-1) were mixed together with the mole ratio of monomer (a1-1-2), monomer (a2-1-1) and monomer (a3-1-1)=50:25:25, and propyleneglycolmonomethylether acetate was added thereto in the amount equal to 1.5 times by mass of the total amount of monomers to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 1.0% by mole and 3.0% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reacted mixture was poured into a large amount of a mixture of methanol and water to precipitate a resin. The obtained resin was filtrated. Thus obtained resin was dissolved in another propyleneglycolmonomethylether acetate to obtain a solution, and the solution was poured into a mixture of methanol and water to precipitate the resin. The obtained resin was filtrated. These operations were repeated three times, to obtain a copolymer having a weight average molecular weight of about 9100, in 66% yield. This resin, which had the structural units of the following formulae, was referred to as Resin A2.

Synthesis Example 6: Synthesis of Resin X1

Monomer (a4-1-7) was used, and dioxane was added thereto in the amount equal to 1.5 times by mass of the total amount of the monomer to obtain a solution. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the solution in the amounts of 0.7% by mole and 2.1% by mole respectively with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 70° C. Then, the obtained reacted mixture was poured into a large amount of a mixture of methanol and water to precipitate a resin. The obtained resin was filtrated. Thus obtained resin was dissolved in another dioxane to obtain a solution, and the solution was poured into a mixture of methanol and water to precipitate the resin. The obtained resin was filtrated. These operations were repeated three times, to obtain a copolymer having a weight average molecular weight of about 18000, in 77% yield. This resin, which had the structural units of the following formula, was referred to as Resin X1.

Synthesis Example 7: Synthesis of Resin X2

Monomer (a5-1-1) and monomer (a4-0-12) were mixed together with the mole ratio of monomer (a5-1-1) and monomer (a4-0-12)=50:50, and methylisobutylketone was added thereto in the amount equal to 0.6 times by mass of the total amount of monomers to obtain a solution. Azobis(2,4-dimethylvaleronitrile) was added as an initiator to the solution in the amount of 3% by mole with respect to the total amount of monomers, and the resultant mixture was heated for about 5 hours at 75° C. Then, the obtained reacted mixture was poured into a large amount of a mixture of methanol and water to precipitate a resin. The obtained resin was filtrated, to obtain a copolymer having a weight average molecular weight of about 15000, in 88% yield. This resin, which had the structural units of the following formulae, was referred to as Resin X2.

(Preparing Resist Composition)

Resist compositions were prepared by mixing and dissolving each of the components shown in Table 1, and then filtrating through a fluororesin filter having 0.2 μm pore diameter.

TABLE 1 Acid Weak Acid Resin Generator (B) Salt (a) Inner Salt Resist Comp. (parts) (parts) (parts) (D) (parts) PB/PEB Composition 1 X1/A1 = 0.7/10 B1-5 = 0.20 I-1 = 0.4 D1 = 0.28 90° C./85° C. Composition 2 X1/A1 = 0.7/10 B1-21/B1-22 = I-1 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 3 X1/A1 = 0.7/10 B1-21/B1-22 = I-2 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 4 X1/A1 = 0.7/10 B1-21/B1-22 = I-3 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 5 X1/A1 = 0.7/10 — I-1 = 0.6 D1 = 0.28 90° C./85° C. Composition 6 X1/A1 = 0.7/10 — I-2 = 0.6 D1 = 0.28 90° C./85° C. Composition 7 X1/A1 = 0.7/10 — I-3 = 0.6 D1 = 0.28 90° C./85° C. Composition 8 X1/A2 = 0.7/10 — I-1 = 0.6 D1 = 0.28 110° C./105° C. Composition 9 A2 = 10 — I-1 = 0.6 D1 = 0.28 110° C./105° C. Composition 10 X2/A1 = 0.7/10 B1-21/B1-22 = I-1 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 11 X2/A1 = 0.4/10 B1-21/B1-22 = I-1 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 12 X2/A1 = 0.4/10 B1-21/B1-22 = I-4 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 13 X2/A1 = 0.4/10 B1-21/B1-22 = I-5 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 14 X2/A1 = 0.4/10 B1-21/B1-22 = I-6 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 15 X2/A1 = 0.4/10 B1-21/B1-22 = I-7 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Composition 16 X2/A1 = 0.4/10 B1-21/B1-22 = I-8 = 0.2 D1 = 0.28 90° C./85° C. 0.95/0.20 Comp. Comp. 1 A2 = 10 IX-1 = 0.60 — D1 = 0.28 110° C./105° C. <Resin>

Resins: Resins A1 to A2, X1 to X1 prepared by Synthesis of Resin

<Salt (a)>

<Acid Generator (B)>

IX-1: The following salt, which was prepared according to the method described in the Examples of JP2011-37837A

B1-5: Salt represented by the formula (B1-5)

B1-21: Salt represented by the formula (B1-21)

B1-22: Salt represented by the formula (B1-22)

<Weakly Acidic Inner Salt (D)>

D1: The following salt, which was a product of Tokyo Chemical Industry Co., LTD

<Solvent of Resist Composition>

Propyleneglycolmonomethylether acetate 265 parts  Propyleneglycolmonomethylether 20 parts 2-Heptanone 20 parts γ-butyrolactone 3.5 parts  (Producing Negative Resist Patterns)

A composition for an organic antireflective film (“ARC-29”, by Nissan Chemical Co. Ltd.) was applied onto 12-inch silicon wafer and baked for 60 seconds at 205° C. to form a 78 nm thick organic antireflective film.

One of the resist compositions was then applied thereon by spin coating in such a manner that the thickness of the film after drying (pre-baking) became 100 nm.

The obtained wafer was then pre-baked for 60 sec on a direct hot plate at the temperature given in the “PB” column in Table 1.

The film was exposed through a mask for forming trench patterns (pitch 120 nm/trench width 40 nm) stepwise with changing exposure quantity, by an ArF excimer laser stepper for immersion lithography (“XT:1900Gi” by ASML Ltd.: NA=1.35, Annular σ_(out)=0.85 σ_(in)=0.65 XY-pol.), on the wafers on which the resist film had thus been formed. Ultrapure water was used for medium of immersion.

After the exposure, post-exposure baking was carried out for 60 seconds at the temperature given in the “PEB” column in Table 1.

Then, development was carried out with butyl acetate (a product of Tokyo Chemical Industry Co., LTD) at 23 degree C. for 20 seconds in the manner of dynamic dispensing method to obtain negative resist patterns.

Effective sensitivity was represented as the exposure quantity at which a resist pattern with 40 nm trench width was obtained.

(Line Edge Roughness (LER) Evaluation)

Irregularities in each wall surface of the obtained resist patterns was observed using a scanning electron microscope.

The symbol “∘” was given when width of irregularities was 4 nm or less,

The symbol “x” was given when the width of irregularities was more than 4 nm.

Table 2 illustrates the results thereof. The parenthetical number means the value of width of irregularities (nm).

TABLE 2 Resist Composition LER Ex. 9 Composition 1 ∘(3.00) Ex. 10 Composition 2 ∘(2.88) Ex. 11 Composition 3 ∘(2.82) Ex. 12 Composition 4 ∘(3.04) Ex. 13 Composition 5 ∘(3.21) Ex. 14 Composition 6 ∘(3.08) Ex. 15 Composition 7 ∘(3.32) Ex. 16 Composition 8 ∘(3.78) Ex. 17 Composition 9 ∘(3.76) Ex. 18 Composition 10 ∘(2.84) Ex. 19 Composition 11 ∘(2.78) Ex. 20 Composition 12 ∘(2.72) Ex. 21 Composition 13 ∘(2.76) Ex. 22 Composition 14 ∘(2.75) Ex. 23 Composition 15 ∘(2.68) Ex. 24 Composition 16 ∘(2.93) Comparative Ex. 1 Comparative Comp. 1 x(4.02)

The salt (a) can be used for a resist composition which is capable of providing a resist film with less line edge roughness (LER) and useful to a fine processing to semiconductors. 

What is claimed is:
 1. A salt having a group represented by formula (a2):

wherein X^(a) and X^(b) each independently represent an oxygen atom or a sulfur atom, X¹ represents a divalent group having an alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group, and where a hydrogen atom contained in the divalent group may be replaced by a hydroxy group or a fluorine atom, ring W represents a C₃ to C₃₆ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom, a sulfur atom, a carbonyl group or a sulfonyl group and where a hydrogen atom may be replaced by a hydroxy group, a C₁ to C₁₂ alkyl group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group, a C₆ to C₁₀ aromatic hydrocarbon group or a combination thereof, L^(b1) represents a C₁ to C₂₄ divalent saturated hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group and where a hydrogen atom may be replaced by a fluorine atom or a hydroxy group, and Q¹ and Q² independently represent a fluorine atom or a C₁ to C₆ perfluoroalkyl group.
 2. The salt according to claim 1, wherein the ring W is a ring represented by formula (a1-1), formula (a1-2) or formula (a1-3:

in each of the formulae (a1-1), (a1-2) and (a1-3), a methylene group may be replaced by an oxygen atom, a sulfur atom, a carbonyl group or a sulfonyl group, and a hydrogen atom may be replaced by a hydroxy group, a C₁ to C₁₂ alkyl group, a C₁ to C₁₂ alkoxy group, a C₃ to C₁₂ alicyclic hydrocarbon group, or a C₆ to C₁₀ aromatic hydrocarbon group.
 3. The salt according to claim 1, wherein L^(b1) is *—CO—O—(CH₂)_(t)—, where t represents an integer of 0 to 6, and * represents a binding site to —C(Q¹)(Q²)-.
 4. The salt according to claim 1, wherein X¹ is a divalent group represented by formula (X¹-1), by formula (X¹-2), by formula (X¹-3), or by formula (X¹-4):

wherein R¹, R², R³, R⁴, R⁵ and R⁶ each independently represent a C₅ to C₁₂ alicyclic hydrocarbon group where a methylene group may be replaced by an oxygen atom or a carbonyl group and where a hydrogen atom may be replaced by a hydroxy group or a fluorine atom, and * represents a binding site to X^(a) and X^(b).
 5. An acid generator, which comprises the salt according to claim
 1. 6. A resist composition comprising the acid generator according to claim 5 and a resin having an acid-labile group.
 7. The resist composition according to claim 6, further comprising a salt which generates an acid weaker in acidity than an acid generated from the acid generator.
 8. A method for producing a resist pattern comprising steps (1) to (5); (1) applying the resist composition according to claim 6 onto a substrate; (2) drying the applied composition to form a composition layer; (3) exposing the composition layer; (4) heating the exposed composition layer, and (5) developing the heated composition layer. 